UV-curable Coatings Research Articles

Physico-mechanical characterisation of basecoats for tailored UV-cured multilayered wood coating systems

The durability and aesthetic properties of wood flooring arise from the properties of the coating applied on its surface. Due to their fast-curing speed, high crosslinking density and high durability, UV-curable coatings are often preferred for flat surfaces such as hardwood flooring, tabletops and doors. In the case of hardwood flooring, several types of deteriorations on the coating surface can shatter the perception of the whole product. In the present work, UV-curable formulations with various monomer-oligomer couples were prepared and used as a basecoat within a multilayered wood finishing system. While the topcoat is designed to endure most of the in-use loads, elastic and plastic stresses can reach deeper layers. The aim of this study is to analyze the influence of basecoat composition and thickness on the mechanical behavior of a UVcurable multilayered wood finishing system. First, physical properties such as the average theoretical segment length, glass transition temperature and crosslinking density, of standalone films of the various monomer-oligomer couples were investigated. Then, indentation and scratch resistance tests were performed to understand the role of the basecoats in the overall mechanical response of the multilayered coatings. The thickness of the basecoat applied was found to have a great influence on the mechanical resistance of the finishing system. No direct correlation was established between the basecoat as standalone films and within the multilayered coatings, considering the complexity of such systems several behaviors were detected. A finishing system able to promote overall good scratch resistance and good indentation modulus was obtained for a formulation displaying an equilibrium between the network density and the elasticity.

A Self-Cleaning UV-Cured Organic Coating with ZnO–Ag Hybrid Nanoparticles

A Self-Cleaning UV-Cured Organic Coating with ZnO–Ag Hybrid Nanoparticles

UV-curable epoxy acrylate composite coatings with high flexibility, super-hydrophobicity, wear-resistance and self-healing property

Photo-curing coating has the advantages of environmental friendliness, short curing time, high productive efficiency and low energy consumption. However, it is also a challenge to overcome the weakness of brittleness, water vapor damage and repairing difficulty. Herein, we have prepared a flexible and self-healing epoxy acrylic coating by introducing dynamic disulfide bond and dangling chain into the resin system, furthermore, sprayed nano-SiO2 to construct the micro surface structure to endow the coating with super-hydrophobicity. The introduction of dynamic disulfide bond has endowed the coating with self-healing ability, while the diluent as dangling chain has promoted the mobility of molecular chain, more importantly, which not only improved the self-healing efficiency of the coating, but also reduced the brittleness, three birds with one stone. Moreover, silane coupling agent was used to modify the nano-SiO2 particles to enhance the abrasive resistance of the coating. The coating exhibits outstanding comprehensive performance: the water contact angle can reach 155°, the self-healing efficiency can reach 97 %, wear-resistance greatly increases by 40 %. These results are expected to provide some references for developing UV-curable coating with high performance.

Preparation of epoxy-based silicone prepolymers with applications in UV-curable coatings

PurposeThis paper aims to investigate the effects on coatings performance in the epoxy silicone resin system owing to the existence of the different chain length of open-chain epoxy monomer. In this paper, [4-Methylphenyl-(4–(2-methylpropyl) phenyl)]iodonium as photoinitiator was added into epoxy silicone resin by ultraviolet (UV)-cured polymerization to investigate the effects on coatings performance owing to the existence of the different chain length of open-chain epoxy monomer.Design/methodology/approachA simple hydrosilylation reaction was used to synthesize epoxy-based silicone prepolymers by using hydrogen-terminated polydimethylsiloxane, 1,2-epoxy-5-hexene, 1,2-epoxy-7-octene and 1,2-epoxy-9-decene as precursors.FindingsThe results revealed that the glass transition temperatures (Tg) and hydrophobicity increased with the chain length of open-chain epoxy monomer in the UV curable epoxy-based silicone coatings, and these films had excellent heat resistance, hydrophobicity, antigraffiti and ink removal properties.Research limitations/implicationsThe cationic photocuring systems are not susceptible to the effect of oxygen inhibition. However, the limitation of cationic light curing process is that it requires a long curing time.Originality/valueThe coatings prepared via the UV curing approach can provide superior antismudge effects, and thus they are promising candidates for use in various industries, especially in fields such as antismudge coatings and antigraffiti coatings.

Antistatic epoxy acrylate/graphene oxide UV-curable coatings with improved shrinkage and adhesion strength

This study presents a simple method for preparing antistatic UV curable coating based on graphene oxide (GO). For this aim, epoxy acrylate (EA) was selected as a UV-curable matrix and synthesized GO nanoplates were dispersed in the resin through solvent-mediated dispersion. Simultaneous crosslinking of UV-curable resin and photoreduction of GO nanoplatelets take place during UV irradiation. The effect of UV intensity and concentration of graphene oxide on the curing kinetics of UV-curable nanocomposite and reduction of GO nanoplatelets was investigated. The results show that the curing reactions of the UV-curable system are disturbed by GO nanoparticles to some extent (depending on UV intensity). They also show that the electrical resistance of the UV-cured EA/GO nanocomposites decreases during the UV curing process. It was found that the shrinkage of the formulations improved considerably with the incorporation of GO into the formulations. The adhesion strength of the cured EA/GO coatings to mild steel was also found to be significantly higher than that of EA coating.

A New Phosphorous/Nitrogen-Containing Flame-Retardant Film with High Adhesion for Jute Fiber Composites.

In this work, a novel P/N flame-retardant monomer (PDHAA) was synthesized through reacting phenyl dichlorophosphate (PDCP) with N-hydroxyethyl acrylamide (HEAA). The structure of PDHAA was confirmed using Fourier transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance (NMR) spectroscopy. PDHAA monomer and 2-hydroxyethyl methacrylate phosphate (PM-2) monomer were mixed at different mass ratios, to prepare UV-curable coatings, and then applied to the surface of fiber needled felts (FNFs), to improve their flame retardancy. PM-2 was introduced to reduce the curing time of the flame-retardant coatings and improve the adhesion between the coating and the fiber needled felts (FNFs). The research results indicated that the surface flame-retardant FNFs had a high limiting oxygen index (LOI) and rapidly self-extinguished in a horizontal combustion test and passed a UL-94 V-0 test. At the same time, the CO and CO2 emissions were greatly reduced, and the carbon residue rate was increased. In addition, the introduction of the coating improved the mechanical properties of the FNFs. Therefore, this simple and efficient UV-curable surface flame-retardant strategy has broad application prospects in the field of fire protection.

Phytic acid in UV-curable anticorrosive coatings

Phytic acid in UV-curable anticorrosive coatings

Eco-Friendly AMPS-Doped Polyaniline/Urethane-Methacrylate Coating as a Corrosion Protection Coating: Electrochemical, Surface, Theoretical, and Thermodynamic Studies

In this study, 2-acrylamido-2-methylpropanesulfonic acid (AMPS)-doped polyaniline (PANI) fibers were used as polymerizable smart anticorrosive agents to prepare eco-friendly UV-curable anticorrosive coatings. For this purpose, AMPS-doped PANI fibers were synthesized through chemical oxidative interfacial polymerization. The size and chemical structure of the prepared conducting fibers were characterized by scanning electron microscopy, 1H NMR, and Fourier transform infrared (FTIR) analyses. As a binder for the prepared conducting fibers, an eco-friendly fluorinated urethane-methacrylate dispersion was synthesized and fully characterized using FTIR analysis. Subsequently, various amounts of the synthesized fibers were mixed with the fluorinated binder to prepare UV-curable anticorrosive coatings. The physicochemical interactions between the PANI fibers and UV-curable binder were studied thoroughly using differential scanning calorimetry and thermogravimetric analyses and measurement of the gel contents and adhesion strength of the prepared composite coatings. The corrosion resistance performance of the prepared coatings was evaluated using electrochemical impedance spectroscopy analysis, and the obtained results revealed that the presence of 2 wt % of the AMPS-doped PANI fibers significantly enhanced the corrosion resistance of the obtained coating. In addition, the corrosion layers of the coatings were analyzed using X-ray photoelectron spectroscopy, which indicated that the AMPS-doped PANI fibers changed the composition of the corrosion product layer. To expand these attempts, this study also explores the interaction of AMPS-doped PANI fibers with the Fe(100) surface using density functional theory as well as atom in molecule calculations. All of the obtained results proved that the outstanding corrosion protection performance of the prepared composite coatings originated from exceptional chemical interactions between the unsaturated doping agents of the prepared PANI fibers and the UV-cured polymer.

Development of bio-based polyester-urethane-acrylate (PUA) from citric acid for UV-curable coatings

Development of bio-based polyester-urethane-acrylate (PUA) from citric acid for UV-curable coatings

Improvement of anti-aging property of UV-curable coatings with silica-coated TiO2

A series of SiO2 coated TiO2 particles (TiO2@SiO2) were prepared by depositing SiO2 layer on the surface of TiO2 particles via an in-situ hydrolysis condensation of tetraethyl silicate, which was used as UV-shielding fillers to prepare UV-curable coatings. The effect of SiO2 layer on the photocatalytic activity, UV-shielding ability and dispersibility of TiO2 particles was systematically explored. The anti-aging property of the UV-cured coating was determined by color change, surface gloss loss, and surface morphology via accelerated UV aging test. It was found that the presence of a continuous and dense SiO2 layer on TiO2 surface could not only improve the dispersibility of TiO2, but also effectively inhibit the photocatalytic activity of TiO2 without sacrificing its UV-shielding ability, thereby significantly enhancing the anti-aging property of UV-curable coatings. Salt spray test shows that the aged UV-cured coating with TiO2@SiO2 exhibited better corrosion protection behavior than the aged pure resin coating as well as the aged TiO2 coating.

Transparent Superhydrophobic Coatings with Mechanical and Chemical Stability Prepared by Modified Polyhedral Oligosilsesquioxanes via UV-Curable Method

Superhydrophobic coating with applicable transmittance was synthesized by simple UV-curable method which was likely suitable for large-scale production. The super-hydrophobicity was derived from the component containing modified polyhedral oligomeric silsesquioxanes which was chosen for low free energy and the potential to form hierarchical structure. The coating adhesion could reach the highest level by strip tape peel test. Compared to the UV-cured commercial coatings, the coating adhesion is enhanced by at least two levels. Super-hydrophobicity was preserved after long duration of water droplet impact, while water contact angle decreased slightly after sand impact due to partial damage of hierarchical structure. The coating can resist chemical corrosion by acid solution (HCl), base solution (NaOH) and salt solution (NaCl). The coating with water repellence function, adequate transmittance, and good mechanical and chemical stability is of great interest for practical outdoor applications.

Novel bio-based phosphorous-containing UV-curable flame-retardant coatings

Novel bio-based phosphorous-containing UV-curable flame-retardant coatings

Study on Press Formability and Properties of UV-Curable Polyurethane Acrylate Coatings with Different Reactive Diluents.

UV-curable coatings have numerous advantages, including environmental sustainability due to 100% solid content, economic feasibility attributable to relatively fast curing time, decent appearance, mechanical properties, chemical resistance, and abrasion resistance. However, UV-curable polyurethane acrylate coatings on metals apparently restrict their engineering applications owing to low mechanical properties and poor thermal stability, giving UV-curable coatings less flexibility and formability. In this study, we evaluated the property change of films according to the type of reactive diluents that lowers the viscosity of UV-curing coatings for pre-coated metal and has a substantial effect on the curing rate, viscoelastic properties, adhesive properties, and flexibility of the film. Moreover, there are many changes in the properties of coatings according to varied curing conditions in order to evaluate the oxygen inhibition phenomenon during the curing process in the atmosphere. In particular, to evaluate the effect of reactive diluents on forming formability, which is the most crucial property for the pre-coated metal, this study used conventional formability tests, such as t-bending or the Erichsen test. Moreover, a cross-die cup drawing mold with a similar form as failure and Safety Zone was utilized in order to obtain clearer information on its actual formability. The analysis on the effect of failure and safety zone on the material used in press forming was conducted by assessing limit punch height and forming a limit diagram of the manufactured film according to varied reactive diluents.

Enhancement of Wood Coating Properties by Adding Silica Sol to UV-Curable Waterborne Acrylics

In recent years, with the development of the coating industry and the increasing awareness of environmental protection, the modification of waterborne wood coatings has become the focus of research. Generally, the system composed of silica sol modification and UV curing can make up for the defects of poor mechanical properties, low hardness, and slow curing speeds of waterborne wood coatings. Herein, we used silica sol-reinforced UV-curable waterborne acrylic wood coatings and tested the related physical properties of the coatings. FT-IR analysis showed that the Si-O-Si bond appeared, indicating that the silica sol was successfully grafted onto the waterborne acrylic molecular chain. The results showed that the mechanical properties of the UV-curable waterborne acrylic wood coating film reached their optimum when the content of silica sol was 1 wt%, the number of UV lamps was 3, and the drying time was 20 min. The corresponding values for wear resistance, hardness, adhesion, and impact strength were 0.106 g (high level), grade 3, and 90 kg·cm, respectively. However, when the content of silica sol is greater than 1 wt%, the related physical properties of the coatings will decrease. The results showed that the gloss of the coating decreased with increasing silica sol content. When the silica sol content was 2 wt%–6 wt%, the coating showed a matte gloss. This present work shows that the modification process is simple, controlled, inexpensive, and meets the demand for UV-curable waterborne acrylic wood coatings in daily life.

Exploiting dynamic thiourethane covalent bonds for enhanced adhesion of UV-curable metal coatings

UV-cured coatings with environmental-friendly trait are widely used in various industries. However, high internal stress during photopolymerization leads to low adhesion of coating, which limits its application on metal surface. In this work, polythiourethane-urethane acrylates (PTUA) with dynamic thiourethane bonds were designed and prepared via click reaction of 3,6-dioxa-1,8-octanedithiol (EDDT) and isophorone diisocyanate (IPDI), following by the reaction between 2-hydroxyethyl acrylate (HEA) and IPDI. By adjusting the IPDI/EDDT/HEA ratios, a series of PTUA with different molecular weights were synthesized. The structure of PTUA was characterized by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR) and gel permeation chromatography (GPC). The incorporation of dynamic thiourethane bonds in UV-cured PTUA coating could release shrinkage stress via dissociative exchange of thiourethane bonds upon heating. After heating, the adhesion strength of the resulting coatings could be significantly improved. The maximum adhesion strength of the PTUA coating could reach 4.90 MPa, which was 2.5-fold increase compared with the coating without heating. This study demonstrated that adaptable thiourethane network was a promising candidate for UV-cured metal coating with enhanced adhesive performance.

Synthesis and characteristics of cardanol-based acrylates as reactive diluents in UV-curing coatings

Two types of cardanol epoxy acrylates (CAR1 and CAR2) were synthesized from bio-based cardanol and used as a reactive diluent. Their dilution effect, curing properties, and thermal and physical properties of UV-cured films as a reactive diluent were compared to those of commercial reactive diluent, 2-phenoxyethyl acrylate (PHEA). CAR series showed a lower dilution effect due to their relatively high viscosity compared to PHEA. However, 10 wt% CAR-diluted films showed similar reactivity and high thermal stability compared to 10 wt% PHEA diluted film, indicating CAR series can be used as partial alternatives to PHEA.

Development of Catalyst-Free Self-Healing Biobased UV-Curable Coatings via Maleate Monoester Transesterification

Developing environmentally friendly UV-curable polymers with multi-functionality is very significant for sustainable development and environmental protection. In this work, a novel tung-oil-based UV-curable oligomer (TOMAH) was synthesized by Diels–Alder and ring-opening reactions via microwave technology. Subsequently, catalyst-free self-healing UV-curable materials based on a maleate monoester transesterification (MMETER) were developed by co-photopolymerization of TOMAH and hydroxyethyl methacrylate (HEMA). The obtained UV-cured materials possessed a high glass transition temperature (Tg > 81 °C), excellent adhesion (grade 1), and flexibility (2 mm). Particularly, the outstanding photopolymerization activity of the UV-curable resins was proved by UV-curing kinetics. In addition, dynamic transesterifications occurred without an external catalyst at a moderate temperature, resulting in good self-healing properties (with a scratch-repair efficiency of 78.6–93.3%) and shape-memory properties for the obtained UV-cured materials. This work combines the multiple advantages of biomass raw material, microwave synthesis technology, UV-curing method, and multifunctional polymers, thus providing an innovative strategy to fabricate sustainable and intelligent coatings.

Toward Large-Scale Energy Harvesting by a UV-Curable Organic-Coating-Based Triboelectric Nanogenerator.

Triboelectric nanogenerators (TENGs) stand out as an attractive form of technology for the efficient harvest of mechanical energy and the powering of wearable devices due to their light weight, simplicity, high power density, and efficient vibration energy scavenging capabilities. However, the requirement for micro/nanostructures and/or complex and expensive instruments hinders their cheap mass production, thus limiting their practical applications. By using a simple, cost-effective, fast spray-coating process, we develop high-performance UV-curable triboelectric coatings for large-scale energy harvesting. The effect of different formulations and coating compositions on the triboelectric output is investigated to design triboelectric coatings with high output performance. The TENG based on a hybrid coating exhibits high output performance of 54.5 μA current, 1228.9 V voltage, 163.6 nC transferred charge and 3.51 mW output power. Moreover, the hybrid coatings show good long-term output stability. All the results indicate that the designed triboelectric coatings show great potential for large-scale energy harvesting with the advantages of cost-effectiveness, fast fabrication, easy mass production and long-term stability.

Improving the decorative performance of UV-curable coatings with iridescent cellulose nanocrystal film.

Cellulose nanocrystals (CNC) possess remarkable mechanical properties, a high aspect ratio, a large specific surface area, and a unique nanostructure, making them a popular choice in various fields. In this study, a CNC suspension was prepared through acid hydrolysis, and subsequently, a film exhibiting iridescence and chiral nematic structure was formed on the cured UV-WA surface via evaporation-induced self-assembly. The mean diameter and length of CNC were determined to be 25.1-33.3 nm and 281.3-404.2 nm, respectively, through transmission electron microscope analysis. The experimental results revealed that the color of the film significantly changes with variations in the CNC suspension concentration. Notably, the formation of the iridescent film is dependent on the concentration of CNC, with concentrations between 1.2% and 2.9% being optimal, and the aspect ratio of the CNC nanoparticles being around 11.3. X-ray diffraction analysis confirmed that the CNC nanoparticles possess the same crystal structure as microcrystalline cellulose (cellulose I). Fourier transform infrared spectroscopy revealed that the C[double bond, length as m-dash]C bond present in the liquid UV-curable coating disappeared upon UV irradiation. The performance of the CNC iridescent film, with varying thickness, was evaluated using UV-vis spectroscopy. The thermogravimetric analysis results indicate that the addition of CNC enhances the membrane's thermal stability and heat resistance. The results indicate that as the thickness of the CNC iridescent film increases, the corresponding UV-vis spectra display a redshift. The UV-WA/CNC shows potential in the field of decoration and establishing a straightforward, cost-effective, and efficient method for producing photonic materials with structural colors.

Preparation of photosensitive phytic acid doped polyaniline and its application in UV-curable anticorrosive coatings

In this paper, photosensitive phytic acid (PAGA) was synthesized via the ring opening reaction of glycidyl methacrylate and phytic acid (PA), which was used to dope polyaniline (PANI). The doped polyaniline (PAGA/PANI) was added to UV-curable resin to prepare UV-curable polyaniline anticorrosive coating. The doping of PANI by PAGA can effectively improve the dispersion of PANI in coatings. Even when the amount of PAGA/PANI increased to 2.0 wt%, PANI can still achieve uniform dispersion in the UV-curable resin. The gel content test showed that with the addition of PAGA/PANI, the curing degree of the UV-cured coating did not decrease, but slightly increased, which was attributed to the introduction of multiple photosensitive groups in PAGA, compensating for the negative effect caused by PANI. The incorporation of PAGA/PANI can also enhance the adhesion of the UV-cured coating due to the presence of phosphonic group in PAGA. With the increase of the content of photosensitive groups, the adhesion of the coating showed an increasing trend. The corrosion resistance of the coating was investigated by electrochemical impedance spectroscopy, and salt spray experiments. The impedance value of the PAGA/PANI coating was two orders of magnitude higher than that of pure resin coating during 30 days of immersion, and neither rust nor blister were observed in the salt spray test for 1000 h, suggesting the significantly enhanced anti-corrosion performance with the incorporation of PAGA/PANI.