Effect of Molecular Weight of Poly(tetramethylene glycol) on Waterborne Polyurethane Dispersion Coating Gloss
Effect of Molecular Weight of Poly(tetramethylene glycol) on Waterborne Polyurethane Dispersion Coating Gloss
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DOI：
10.1002/bkcs.11864
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发表时间：
2019-09-09
影响因子：
1.7
通讯作者：
Lee, Youn-Sik
中科院分区：
文献类型：
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作者：
Bhattarai, Saurabha;Lee, Sung-Il;Lee, Youn-Sik
最初，高光泽水性聚氨酯（WPU）涂料由于其广泛的应用而占据了市场主导地位。然而，低光泽WPU涂料最近在特定的功能和装饰应用中也受到越来越多的关注。1-3例如，低光泽WPU涂料减少了表面眩光，特别是在汽车内部，电器和电子电器，木材或家具表面。与高光涂层相比，低光泽WPU涂层还有助于隐藏划痕和缺陷。4，5传统上，外部消光剂如二氧化硅颗粒、粘土、沸石和其他粉末已被用于通过增加涂层表面的粗糙度来实现低光泽度。然而，消光剂由于与有机组分聚氨酯（PU）的不相容性而在WPU中分散不良，导致涂层表面上的光泽不均匀。无机消光剂与PU的不相容性还引发消光剂颗粒从涂层表面的最终挤出，导致在间歇使用后消光剂效果的损失。8近年来引入的一种新方法是在粗糙的薄膜上形成微米级颗粒，从而制备低光泽涂层，这会导致入射光的强烈弯曲和辐射扩散，导致透光率差和光泽度低。然而，迄今为止，文献中仅报道了少数研究。例如，Yong等人获得了基于PU-丙烯酸酯混合乳液的低光泽度涂层，尽管具有高光泽度（在60 °下为3）。9 Li等人制备了单组分WPU消光树脂。简言之，NCO封端的PU预聚物通过异佛尔酮二异氰酸酯（IPDI）、聚（四亚甲基二醇）（PTMEG）和丙酸（DMPA）之间的反应，然后用三乙胺（Et 3 N）中和来合成。预聚物通过2-[（2-氨乙基）氨基]乙磺酸钠盐（A95）扩链，然后加入肼。A95具有扩链和乳化的双重作用。通过改变各种反应物的比例来优化反应条件，在将WPU应用于皮革时，得到60光泽度为1.5和透光率为9%。最近，Cao等人使用Li等人报道的非常类似的程序制备WPU分散体，除了他们使用聚（己二酸1，4-丁二醇酯）二醇（PBAG）代替PTMEG。除了IPDI、PTMEG和DMPA之外，他们还使用三羟甲基丙烷（TMP）来形成NCO封端的预聚物。他们报道了TMP增加了微相分离，因此降低了透明度和光泽度（1，60）。在各种商业二醇中，Li等人和Cao等人分别使用平均分子量为1000的PTMEG和PBAG。然而，PU的软域和硬域之间的相分离也在很大程度上受二醇的分子量以及化学结构的影响。12在PTMEG的情况下，三种不同的分子量（1000、2000和2900：分别为PTMEG-1000、PTMEG-2000和PTMEG-2900）是可商购的。最初，我们使用PTMEG-2000和TMP制备WPU分散体，按照Cao等人报道的略微修改的程序。然而，WPU分散体中的聚合物颗粒在几天内沉降，表明分散体对于实际应用是不稳定的，主要是由于PTMEG-2000与PBAG相比亲水性降低。在这项研究中，我们根据Li等人报道的程序制备了单组分WPU分散体，使用PTMEG-1000、PTMEG-2000和...
Initially high-gloss waterborne polyurethane (WPU) coatings have dominated the market because of their wide application. However, low-gloss WPU coatings have also received increased attention lately for specific functional and decorative applications. 1–3 For example, low-gloss WPU coating reduces the surface glare, especially in the interior of automobiles, electrical and electronic appliances, wood or furniture surfaces. Low-gloss WPU coating also facilitates hiding of the scratches and imperfections, when compared with high-gloss coating. 4, 5 Traditionally, external matting agents such as silica particles, clays, zeolites, and other powders have been used to achieve low gloss by increasing the roughness of the coating surface. 6, 7 However, the matting agents are poorly dispersed in WPU due to incompatibility with the organic constituent polyurethane (PU), resulting in gloss inhomogeneity on the coating surface. The incompatibility of inorganic matting agents with PU also triggers eventual extrusion of the matting particles from the coating surface, leading to the loss of matting effect after intermittent use. 8 A new method introduced in recent years entails preparation of low-gloss coating based on the formation of micronsized particles on the rough film, which causes strong bending of incident light and radiation diffusion, leading to poor light transmittance and low gloss. However, only a few studies have been reported in the literature till date. For example, Yong et al. obtained low-gloss coating based on PU-acrylate hybrid emulsion, albeit with high gloss (3 at 60). 9 Li et al. prepared a single-component WPU matting resin. 10 Briefly, NCO-terminated PU prepolymer was synthesized via reaction between isophorone diisocyanate (IPDI), poly (tetramethylene glycol)(PTMEG), and propionic acid (DMPA), followed by neutralization with triethylamine (Et3N). The prepolymer was chain-extended by 2-[(2-aminoethyl) amino] ethane sulfonic acid sodium salt (A95), followed by the addition of hydrazine. A95 plays a dual role including chain-extension and emulsification. The reaction conditions were optimized by varying the ratios of various reactants, resulting in a 60 gloss of 1.5 and light transmittance of 9% upon application of WPU to leather. More recently, Cao et al. prepared WPU dispersions using a very similar procedure reported by Li et al., except that they used poly (1, 4-butylene adipate) glycol (PBAG) instead of PTMEG. 11 They used trimethylol propane (TMP) in addition to IPDI, PTMEG and DMPA for the formation of NCO-terminated prepolymer. They reported that TMP increased the microphase separation and hence, decreased transparency and gloss (1 at 60). Among various commercial glycols, Li et al. and Cao et al. used PTMEG and PBAG with an average molecular weight of 1000, respectively. However, the phase separation between the soft and hard domains of PU is also largely affected by the molecular weight as well as the chemical structure of diols. 12 In the case of PTMEG, three different molecular weights (1000, 2000, and 2900: PTMEG-1000, PTMEG-2000, and PTMEG-2900, respectively) are commercially available. Initially, we prepared WPU dispersions using PTMEG-2000 and TMP by following the slightly modified procedures reported by Cao et al. However, the polymer particles in the WPU dispersions settled down within several days, indicating that the dispersion was unstable for practical applications, mainly due to reduced hydrophilicity of PTMEG-2000 compared with PBAG. In this study, we prepared single-component WPU dispersions based on the procedures reported by Li et al., using PTMEG-1000, PTMEG-2000, and …