The molecules of waterborne polyurethane are not simply dissolved in water. Instead, a large number of molecules are aggregated into spherical colloidal particles floating in water, which prevents colloidal particles from precipitating and forms stable polyurethane dispersions through affinity between colloidal particles and water.

從以上圖我們可以看到，聚氨酯粒子能夠在水中穩(wěn)定存在是依靠粒子自身重力和粒子與水的親和力的平衡。若親和力大于或等于重力，則粒子可以穩(wěn)定存在，樹(shù)脂亦可穩(wěn)定；若親和力小于重力，則粒子沉降，樹(shù)脂則發(fā)生沉淀或分層。
From the above picture, we can see that the stability of the polyurethane particles in the water depends on the equilibrium between the particle's own gravity and the affinity of the particles to the water. If the affinity is greater than or equal to the gravity, the particles will be stable and the resin will be stable. If the affinity is less than the gravity, then the particles will sink and the resin will precipitate or stratified.

二，如何保證聚氨酯樹(shù)脂有足夠的親和力。
Two, how to ensure that the polyurethane resin has sufficient affinity.
現(xiàn)在通常的作法是在水性聚氨酯的分子鏈中接入和水有親和力的基團(tuán)或鏈段，一般是帶有陽(yáng)離子、陰離子或非離子鏈的材料。若聚氨酯分子中接入的是陽(yáng)離子，則該法制得的水性聚氨酯為陽(yáng)離子型，陰離子和非離子亦然。這些親水基團(tuán)或鏈段處于聚氨酯粒子表面，形成帶電層或膠體層對(duì)粒子產(chǎn)生包覆效果，且相鄰粒子的保護(hù)層相互排斥，防止粒子團(tuán)聚而失穩(wěn)。
Now, the usual way is to connect the molecular chains of waterborne polyurethane and water with affinity groups or segments, usually with cationic, anionic or non-ionic chains. If the polyurethane molecules are connected with cations, the aqueous polyurethane obtained by this method is cationic, anionic and nonionic. These hydrophilic groups or segments are on the surface of polyurethane particles, forming charged or colloidal layers to produce particles, and the protective layers of neighboring particles repel each other to prevent particle aggregation from destabilizing.

三，高固含和低固含水性聚氨酯穩(wěn)定體系的差別。
Three, the difference between high solid and low solid water bearing polyurethane stabilizer system.
高固含水性聚氨酯粒子往往比低固含的大很多，一般認(rèn)為30%固含樹(shù)脂的粒徑在50nm左右，而50%以上固含樹(shù)脂的粒徑往往大于200nm，這樣導(dǎo)致粒子自身重力往往大很多，根據(jù)重力/親和力平衡原理，高固含樹(shù)脂的粒子與水應(yīng)具有更強(qiáng)的親和性。為了維持較強(qiáng)的穩(wěn)定性，聚氨酯粒子必須具有更強(qiáng)的保護(hù)層，所以必須選擇更強(qiáng)電解性粒子或鏈段接入聚氨酯分子中。
High solid aqueous polyurethane particles are much larger than the low solid content, generally 30% solid resin particle size of about 50nm, while more than 50% solid resin particle size is greater than 200nm, so that the particle gravity often much larger, according to the gravity / affinity balance principle, particle and water resin with high solid content should have a stronger affinity. In order to maintain strong stability, polyurethane particles must have stronger protective layer, so we must choose stronger electrolytic particles or segments to access polyurethane molecules.

高固含和低固含水性聚氨酯穩(wěn)定體系的差別。

水性聚氨酯已經(jīng)發(fā)展了數(shù)十年，上世紀(jì)60年代，美國(guó)、德國(guó)等發(fā)達(dá)國(guó)家就著手水性聚氨酯的研究，中國(guó)在這方面研究較晚，真正開(kāi)始系統(tǒng)性研究是在改革開(kāi)發(fā)以后。經(jīng)過(guò)數(shù)十年的發(fā)展，我國(guó)的水性聚氨酯已取得長(zhǎng)足的進(jìn)步，但與發(fā)達(dá)國(guó)家相比，差距還是很明顯的，特別是高性能特種化產(chǎn)品相對(duì)偏少，基礎(chǔ)研究沒(méi)有形成系統(tǒng)性。
Waterborne polyurethane has been developing for decades. In the 60s of last century, the developed countries such as the United States and Germany began to study waterborne polyurethane. China's research in this field is rather late. The real systematic research is after the reform and development. After decades of development, China's waterborne polyurethane has made great progress, but compared with developed countries, the gap is still very obvious, especially the high performance special products are relatively few. Basic research is not systematic.

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