Pigment dispersion: Pigment dispersion assessment

评价分散程度是建立标准配方、很好的操作方法和品质控制的关键。评估分散程度要看聚集体分离是否完全,分离后是否絮凝。白色和有色颜料有效的评估方法是比较着色力。

对白色分散体,可称出少量样品与少量标准有色分散体如蓝色进行混合,同时以相同比例把标准白和该标准蓝11昆合后,在白纸上把这两个着色样品相邻放置,用刮刀一起下刮,可比较两样品的颜色。如果产物比标准的颜色深,则这批白色分散体的着色力低,意味着分散程度不好。对有色分散体如蓝色,可用相同步骤,只是标准蓝和产品蓝都与相同比例的标准白混合。

同样也可以评估像汽车金属色涂料之类的颜料分散体,将标准和样品在玻璃板上相邻并排刮,用目测或仪器测量来评估雾影程度或与标准的差别。

检验絮凝可将用于测定着色力的着色浆流涂在马口铁板上,用食指轻刮。如果颜色有变化,则分散体已絮凝。一个白和蓝颜料的混合物,被刮处变得更蓝,则蓝颜料已絮凝;变得更浅,则白颜料已絮凝。絮凝也可从分散体的流动来检测。稳定化良好的分散体的流动性是牛顿型的,如果是剪切变稀的(设计上不含剪切变稀组分)则是絮凝了。

另一评估颜料分散的方法是离心沉降法。沉降速度决定于颗粒大小和分散相与介质的密度差。分离好、稳定好的分散体沉降分离慢,但完全沉降后,沉降物量少。分离好而稳定差的分散体沉降快,沉降物庞大。因为絮凝物沉降较快,又因为包着连续相,故形成庞大的沉降物。絮凝的沉降物搅拌或摇动后比未絮凝的易恢复到均匀的悬浮。如果颜料较快地沉降或离心成结实的一层,那是分离未完全,因为在沉降物中聚集体较大,所以沉降更快。对于开发工作和产品品质控制,离心沉降试验能够给出足够的定性或半定量信息。作为研究,可以测定定量数据,从离心速度计算絮凝程度。用显微镜检验分散体时需要注意样品的制备过程,在使用溶剂稀释样品时,则有可能发生絮凝,就不一定是颜料造成的絮凝。

The flocculation gradient technique may be a fast and accurate method for the quantitative study of the degree of pigment dispersion in liquid and dry paint films. This method uses 2500nm infrared light to measure the relationship between the scattering degree of the paint film and the film thickness. Particles scatter longer wavelength light stronger than visible light, and the refractive index difference between pigment and binder is more significant at 2500nm. A plot of scattering versus film thickness gives a straight line whose slope increases with increasing flocculation. This technique has proven useful for the determination of flocculation of various pigments [Ha11JE, BenoitR, etc. JCoatTechno1, 1988, 60(756): 49.]. Infrared reflectometry can also be used to determine the degree of flocculation of liquid dispersion samples.

The method widely used in the paint industry to measure the grinding fineness is the scraper Fineness Meter, which can indicate whether the large pigment aggregates are broken, whether there are foreign particles, etc., and it is fast to test, and it takes about half a minute, but it can be obtained Values ​​of cannot be used to assess dispersion.

Place the dispersion sample before the zero reading on the plate, scrape down with the scraper, then lift the plate, and immediately look across the scraped sample to find on which scale you start to see protruding particles or streaks as the particles scrape down, It is claimed that the larger the reading, the better the dispersion. The instrument cannot measure the degree of dispersion. First, the main problem in making a satisfactory dispersion is preventing flocculation, however it cannot detect flocculation at all because any flocculation is broken when scraped off. Second, properly dispersed pigment particles are much smaller than the groove depth of the fineness gauge. In the total pigment content of a coating, there is only about 0.1% Ti02, and the dispersion cannot pass the Fineness Meter.