TIDAS - Results & Data Display
One of the strengths of the TIDAS system is the manner in which it not only collects the results but more importantly displays them for the end user examples of this can be seen below.Figure 4 shows an example of results achieved on TIDAS. Here a paint of average dispersion is shown. On the left-hand side, the enhanced image of the grind gauge is displayed, with the nibs showing up as white speckles. The histogram to the right is derived from this image, with the dispersion rating and other details displayed beside it.
Figure 4 - Data output from TIDAS
The histogram displays the nib count from each 1mm band of the image as blue bars. However, if more than 50 nibs are counted in one band, the result will be a continuous red bar to warn that the counts are 'off scale'. If very large nibs are encountered in a band, it will be deemed that these are not true nibs, but are more likely to be air bubbles or dust, and the bars will be displayed in green for each large nib found. The algorithm will ignore any of these oversize particles in the calculation of the dispersion rating. The example in Figure 4 shows one of the two drawdowns that were recorded to produce individual ratings of 16um and 17um, and an average rating of 17mm (quoted to the nearest whole number). The reference number and rating for each drawdown, the average rating, and the time and date of recording are displayed to the right of the histogram.
It can also be seen from this example that the algorithm requires a certain number of nibs within adjoining micron bands to determine a dispersion rating and not the first isolated particle.
The mathematical algorithm, which is based on the visual dispersion rating technique of four experienced Huntsman Tioxide technicians, enables TIDAS to give consistent results in good agreement with manual ratings of an experienced, well-trained operator as shown in Figure 5.
Figure 5 - TIDAS correlation with one experienced operator
The image-capture system enables an electronic record of each dispersion to be kept. Such a system is invaluable for quality assurance records, production quality comparisons, and helping with product and process improvement work. Images can also be sent instantaneously to different locations using the electronic mail system.
TIDAS - grind gauge requirements
Though visually similar to commercially available standard gauges, each gauge supplied with TIDAS is manufactured so that the grooves and scale markings on the gauge are positioned to a tighter specification than normal. A calibration block is also provided to ensure the instrument is performing to specification.
The 0-50um grind gauge is used for general testing on TIDAS as this range covers the normal spread of results experienced for good to poor levels of dispersion. However, there are occasions when undispersed particles can exceed, or be close to 50um. In these instances, TIDAS can be used with a 0-100um gauge to allow imaging, and a rating to be obtained. Typically, water based paints or paints containing large particle extenders would be tested on the deeper channel gauge. Conversely, paints showing excellent levels of pigment dispersion may require a more discriminating examination of the nibs present in the paint; TIDAS can therefore also be used with a 0-25um gauge.
The following images produced from the same paint sample when examined on each of the three ranges of grind gauge. Agreement between the 0-25 and 0-50um gauges is good (both give a rating of 16um). The 0-100um gauge is under-rating the dispersion, clearly demonstrating the need to use the most suitable gauge for the level of grind of the paint.
TIDAS - additional data output
Further information can be obtained from TIDAS by downloading the nib count into a spreadsheet or graphics programme, enabling additional data analysis to be undertaken. Figure 7 shows an example of data from TIDAS that has been downloaded for comparative analysis. The nib count is shown for each 1mm dispersion band from 0mm to 50mm for four different pigments. This way of presenting the results allows the dispersion performance for multiple pigments to be compared on the same graph.
Figure 7 - TIDAS dispersion data plotted from spreadsheet
A number count taken from the spreadsheet of the 8-50µm range on the gauge, i.e. the area of perhaps most interest to the paint manufacturer, gives the following results for each of the four pigments:
Pigment 1 (rated 10 um) - 25 nibs
Pigment 2 (rated 16 um) - 118 nibs
Pigment 3 (rated 26 um) - 355 nibs
Pigment 4 (rated 34 um) - 491 nibs
In other words, different types of information can be supplied by TIDAS depending on the requirements of the user.
As with any instrumental analysis the results obtained are dependent on the correct paint preparation. Using TIDAS will not guarantee correct or consistent readings unless the correct paint preparation and application techniques are used and a clean working environment is maintained.