Application of Photoacoustic Fourier Transform Infrared Spectroscopy to Paper coatings for Coat Weight Measurement in Paper coatings Enriched with Organic Polymers, 2005 TAPPI Coating Conference

Herein, we report the use of Photoacoustic Fourier Transform Infrared (PA-FTIR) spectroscopy as an alternative tool for coat weight determination of specialty paper coatings that are rich in organic polymers. We have taken advantage of the ability of PA-FTIR spectroscopic technique in accurately detecting various organic components of a paper coating, and have utilized it for obtaining quantitative coat weight information. When paper samples are coated with formulations that have significant amounts of organic pigments and binders, and at relatively low coat weights as is the case with certain thermal imaging papers, we found that accurate determination of coat weights by conventional methods such as gravimetric methods including oxygen ash were less than satisfactory when the base stock is LWC or ULWC. Variation in base stock weight can often be in the 2-4 gsm range. This variation in base stock can make it very difficult to accurately measure the applied coat weight when the coat weight is very low. In a coating which is low in mineral pigments and high in organic pigments this is especially true as there is very little ash from the coating. In such cases, PA-FTIR proved to be a simple, non-destructive and reliable method for coat-weight determination. Thus, we have applied PA-FTIR technique to LWC sheets coated with formulations having 50-100 parts of organic pigments and latexes, and our results show that the intensity of poly(styrene) stretching band in the infrared region can provide an accurate measurement of the concentration of organic pigment and latexes of the coating which, in turn, can be easily translated to reliable coat weight information.