摘要
随着全人类对环境保护的高度重视,低VOC排放的水性涂料和高固体分涂料以及零污染的粉末涂料逐渐成为世界涂料发展的主流,但粉末涂料和高固体分涂料因施工工艺的特殊而限制了应用,因此,水性涂料正在成为环保性涂料市场的主角。
丙烯酸树脂具有优异的耐光、耐候性、户外曝晒耐久性强,紫外光照射不易分解和变黄,能长期保持原有的光泽和色泽,耐热性、耐腐蚀、耐化学品性能良好,有优异的装饰性能和保护性能,是涂料工业中最受青睐的一类树脂。
纳米材料具有小尺寸效应、表面效应、量子尺寸效应和宏观量子隧道效应等特殊的性质,它的加入可以大大提高涂料的耐冲击、附着力、耐老化、耐腐蚀、抗紫外线等性能。
本实验中合成了水性丙烯酸树脂,加交联剂氨基树脂制成水性汽车罩光清漆,并添加纳米Si02进行改性,主要研究内容包括以下几个方面：
1树脂分子量对漆膜性能的影响
树脂分子量低,粘度小,交联反应可以充分发生,但是因为分子量低,漆膜性能较差,树脂分子量高,粘度较大,交联反应发生不充分。
2树脂不同溶剂对漆膜性能的影响
以丙二醇甲醚和异丙醇按体积比为2：1做溶剂和以正丁醇和异丙醇以质量比为1：1做溶剂,结果第一种溶剂所做漆膜性能明显优于第二种,可见,第一种溶剂对丙烯酸树脂的溶解性更好,交联反应发生得更充分。
3树脂不同单体浓度对漆膜性能的影响
以树脂单体浓度分别为75%、70%、65%和60%做成漆膜,结果发现单体浓度越低,交联反应发生得越充分,但是单体浓度降低,也意味着VOC的排放量增大,所以,单体浓度不能过低。
4树脂高、低分子量不同比例混合对漆膜性能的影响
以高分子量树脂和低分子量树脂的比例为20/80、30/70、40/60、50/50进行混合,并将高分子量树脂分子量上的交联基团增大一倍,以便使成膜的交联网络结构更致密,以此来提升漆膜的各项性能,结果发现,20/80的漆膜耐化学品性能有了大幅度提高,但是机械性能仍不合格,原因是漆膜交联度偏高,将低分子量树脂中交联基团数量适当降低,交联剂用量也相应减少,最后获得的漆膜具有优异的机械性能及耐化学品性能。
5不同纳米Si02含量对漆膜性能影响
将纳米Si02按成膜物质量的0.5%、1%和2%加入清漆中,结果分散后2%的清漆在静置2小时后部分纳米粒子重新团聚沉入瓶底。0.5%的漆膜硬度提高,但冲击强度下降,1%的漆膜冲击强度下降,并且两者的耐化学品的性能均下降。
With human paying great attention to environmental protection, low VOC emissions of water-based paint and high solids coatings and powder coatings of zero-pollution is becoming the mainstream of development of the world paint, powder coatings and high solids coatings were limited application due to the special construction techniques, therefore, the water-based paint is becoming the protagonist of environmentally freidlly coatings market.
Acrylic resin has excellent light resistance and weather resistance, good durability of outdoor exposure, not easy to decompose and turn yellow under UV irradiation, it could maintain original gloss and color for long term and has good heat resistance、corrosion resistance、chemical resistance and excellent performance of decorative and protective, so it has become the most popular resin in coating industry.
Nano-materials have small size effect, surface effect, quantum size effect and macroscopic quantum tunneling effect, adding them to paint can greatly improve the impact resistance、adhesion、resistance to aging、corrosion resistance、UV resistance and other properties of film.
Aqueous acrylic resin was synthesized in this work, using it and crosslinker amino resins made of water-based automotive clearcoats and adding nano-silica to modify, the main contents include the following aspects:
1Effect of molecular weight of resin on film properties
While molecular weight of resin is low, its viscosity is small, the crosslinking reaction can occur, but because of low molecular weight, poor performance of film, in contrast, while molecular weight of resin is high, its viscosity is big, the crosslinking reaction could not occur adequately.
2Effect of different solvent of resin on film properties
Propylene glycol monomethyl ether and isopropyl alcohol by volume ratio of2:1as the solvent and n-butyl alcohol and isopropyl alcohol by mass ratio of1:1as the solvent, results show the film using the first solvent do have better performance than the second, this shows the first solvent have better solubility for acrylic resin, so cross-linking reaction occurs more fully.
3Effect of different monomer concentration of resin on film properties
Films were prepared with monomer concentrations of resin were75%,70%,65% and60%, respectively, it was found that when monomer concentration is low, the crosslinking reaction occurs more fully, but reduces the monomer concentration, also means the VOC emissions increase, therefore, the monomer concentration should not be too low.
4Effect of mixing high and low molecular weight of resin on film properties
High molecular weight resin and low molecular weight resin ratio of20/80,30/70,40/60,50/50were mixed, and the crosslinking groups on the high molecular weight of the resin increases one times, so as to make the cross-linked network structure more compact to promote the performance of film, it was found that the chemical resistance of the film of resin mixing ratio is20/80has been greatly improved, but the mechanical properties are still unqualified, reason is that the crosslinkage of film is too high, so reduce amount of crosslinking groups on low molecular weight resin, the amount of crosslinking agent also reduce appropriately, the film finally has excellent mechanical properties and chemical resistance.
5Effect of different nano-silica content on film properties
0.5%,1%and2%nano-silica of film forming matter weight were added clearcoats, part of nano-silica were conglomerated in2%nano-silica content of clearcoats one hours after dispersing, the hardness of film of0.5%nano-silica content increases, but the impact strength decreases, the hardness and impact strength of filmof1%nano-silica content both decreases, chemical resistance of two film both decreases, this result shows experiment of adding nanoparticles to modify is not successful.
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