UV-curable waterborne polyurethane-acrylate: preparation, characterization and properties

https://doi.org/10.1016/j.porgcoat.2011.08.019Get rights and content

Abstract

The waterborne polyurethane-acrylate (PUA) oligomer was firstly prepared based on isophorone diisocyanate (IPDI), polyether polyol (NJ-210), dimethylol propionic acid (DMPA) and hydroxyethyl methyl acrylate (HEMA) via in situ and anionic self-emulsifying method. The UV-curable polyurethane-acrylate (UV-PUA) was obtained with oligomer, monomers (BA and TPGDA) and photoinitiator Darocur 1173. FT-IR, DSC and TGA were employed to investigate the structures and thermal properties of the UV-PUA films. The effects of BA/TPGDA (R) value, the content of Darocur 1173 and the UV curing time on the performances were investigated. Some mechanical performances, solvent resistance and the gel content of UV-PUA films were measured. When the ratio of BA/TPGDA was 5/5, the UV-PUA film had the best solvent (water, alkali and ethanol) resistances. Besides, with the ratio of the BA/TPGDA increasing, the surface drying time increased. When the content of Darocur 1173 was 4%, the gel content achieved the maximum while the surface drying time achieved the minimum. The obtained UV-curable polyurethane-acrylates are promising as oligomers for UV-curable coatings, plastics, inks and adhesives.

Graphical abstract

. The waterborne UV-PUA emulsion was prepared using UV-PUA oligomer, the Darocur 1173 and the monomers composed of BA and TPGDA. The curing time was very short at room temperature. The obtained UV-PUA films have good hardness, solvent resistance and mechanical properties. It is hopeful that the UV-PUA dispersions can be applied to commercial use in different regions.

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Highlights

► Preparation of UV-PUA oligomer. ► Preparation of UV-PUA film. ► The effect of the ratio of BA/TPGDA on the properties of UV-PUA films. ► The effect of the content of Darocur 1173 on the properties of UV-PUA films. ► The effect of curing time on the properties of UV-PUA films.

Introduction

Polyurethanes (PU) have been found in wide applications such as coatings and adhesives due to their unique properties, and great efforts have been made in chemistry and physics. Waterborne polyurethane (WPU) has been developed largely because of its excellent mechanical properties, fire resistance, low toxicity and lack of environmental hazard, but suffers from poor water and alkali resistance because of the hydrophilic group such as carboxyl group in their molecule chains. Compared with the polyurethane resin, polyacrylate-type products show an outstanding performance in the weatherability, water resistance, and solvent resistance, therefore there is a complementary role in the performance of polyurethane (PU) and polyacrylate (PA). Waterborne polyurethane-acrylate (WPUA) can obtain various properties and enhanced performance resulted from its specific segmented structure and modification with acrylate. And it can be satisfactorily applied in coatings for wood and automobiles, biologic materials, electronic materials, textiles, leather and printing inks [1], [2], [3].

Recently, environmental legislation is increasingly strict with coatings industry. The waterborne coatings using ultraviolet (UV)-curing technology have gained increasing interests due to their advantages such as less environmental pollution, low energy consumption, high chemical stability, cost efficient, high curing speed and very rapid curing even at ambient temperatures [4], [5], [6], [7]. These environmental friendly products are used to reduce the volatile organic compounds (VOC) released to the atmosphere by solvent-borne systems and are expected to exhibit same performance as that of conventional solvent-borne systems [8], [9], [10], [11]. The UV-curable WPUA coating has the features of instant drying, solvent-free formulations, reduced energy consumption, coating on heat sensitive substrate, low space and capital requirement for curing equipment [12], [13], [14], [15], [16], [17], [18]. The UV-curable coatings consist of oligomer, monomer and photoinitiator, so the coating film properties, such as hardness, abrasive resistance, flexibility and weatherability, mainly depend on the oligomer structure and its concentration in the formulation. Therefore, looking for more new structure and special property PUA would play the key role in the development of UV curable chemistry [19]. In the process of photo-polymerization, the content of the photoinitiator would determine the degree of the polymer curing [20]. Besides, the photoinitiated radical polymerization of acrylate resins, the presence of radical scavengers, the reactivity and viscosity of the acrylate formulation, the wavelength and intensity of the UV radiation all could affect the performance of the UV curing film. Studer et al. [21] comprehensively investigated the effect of all these UV curing parameters on acrylate conversion.

In this work, the UV-PUA oligomer was prepared with isophorone diisocyanate (IPDI), polyether polyol (NJ-210), dimethylol propionic acid (DMPA), hydroxyethyl methyl acrylate (HEMA) via in situ and anionic self-emulsifying method; and the UV-PUA system was composed of the oligomer, photoinitiator Darocur 1173 and monomers (BA-TPGDA). The effects of the ratio of the BA/TPGDA, Darocur 1173 and the curing time on the performance of the UV-PUA films were investigated. The UV-PUA films were characterized and analyzed by Fourier transform infrared spectroscopy (FT-IR), Differential scanning calorimetry (DSC), solvent resistance, gel content and mechanical properties.

Section snippets

Materials

Polyether polyols (NJ-210, Mn = 1120 g/mol) was produced by Ningwu Chemical CO., Ltd., in Jurong, Jiangsu, China. Dimethylpropionic acid (DMPA) was produced by PERSTOP Co., in Helsingborg, Sweden. Isophorone diisocyanate (IPDI) was supplied by Rongrong Chemical Ltd., Shanghai, China. Hydroxyethyl methyl acrylate (HEMA) was provided by Yinlian Chemical Ltd., Wuxi, Jiangsu, China. Butyl acrylate (BA), triethylamine (TEA), acetone, dibutylbis (lauroyloxy) tin (DBLT), and N-methyl -2-pyrrolidone (NMP)

The effect of ratio of BA/TPGDA (R) on the properties of UV-PUA films

Fixed the content of the Darocur 1173 (3%), NCO:OH ratio (2.0) and the weight of the PUA oligomer (10.8 g), a series of UV-PUA films were prepared through changing the R value. The proportion of the UV-curable was listed in Table 1.

Conclusion

The waterborne UV-PUA emulsion was prepared using UV-PUA oligomer, the Darocur 1173 and the monomers composed of BA and TPGDA. The proportion of BA and TPGDA, the content of the Darocur 1173 and the curing time were important effects on the properties of the cured films. The experimental results indicated that the optimum irradiation time was 30–40 s after the coatings being painted on a poly (tetrafluoroethylene) plate at room temperature, the ratio of the BA/TPGDA was 5/5, and initiator dosage

Acknowledgement

This project was supported by the Agricultural Independent Innovation of Jiangsu Province (CX(11)2032), Jiangsu Planned Projects for Postdoctoral Research Funds (1002033C) and Jiangsu Province Key Laboratory of Fine Petro-chemical Technology (213164).

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