Method and apparatus for quantifying pigment dispersion quality by paint drawdown

摘要

An automated computer-controlled method and apparatus for measuring the quality or fineness of a pigment dispersion sample, comprising placing the pigment dispersion at the deep end of the tapered path of a Hegman gage block, placing the Hegman gage block in a holder in a motorized drawdown device that draws the scraper along the length of the tapered path at an angle and to at a contact pressure and at a controlled rate, thereby creating a tapered film sample of paint whose thickness tapers from a maximum thickness of 100 micrometers to a minimum thickness of zero. An illuminator assembly illuminates the sample with a substantially collimated light source at an intensity level and the light reflected from the sample is collected by a lens onto a photodetector array in a digital camera. After a time interval the camera acquires an image of the sample. The image is digitized and stored in a memory in the computer and then a portion of the image within a region of interest corresponding to the sample in the tapered path is analyzed to detect and count pigment agglomerates that protrude above the surface of the sample.