Mechanical Testing of Coated Paper Systems

Understanding the mechanical nature of coated paper systems is critical to optimizing the manufacturing process and controlling the final product properties. The purposes of this study are to develop tests capable of quantifying the mechanical properties of the coated papers, a quality control test to predict dusting, and to determine the effects of coating formulation and paper processing changes on these mechanical properties. Four tests were developed to quantify the mechanical nature of coated papers. An elastica bending stiffness test was used to measure the modulus of the coatings in the tensile direction. This test was also modified to account for and quantify the viscoelastic nature of coatings. A low load indentation test was used to determine the coating modulus in compression. Two tests were developed to measure the dust generated during a slitting operation: one using a straight edge and one using a rotary cutter. Seventeen variations in coating formulation and laboratory processing parameters were produced. Coating variations included changes in styrene-butadiene latex binder level, binder type, pigment type, and laboratory drying method. These samples were all run using the tests described above. Pigment shape is found to influence both the tension and compression moduli. The trends for these two parameters are inverses of each other: tension modulus increased with increasing pigment shape factor but compression modulus decreased. This result agrees with recent work reported in the literature. Starch increases both the tension and compression moduli. A decrease in latex particle size resulted in an increase in compression modulus. No trend was apparent for changes in binder glass transition temperature under the laboratory conditions. Drying method had little effect on tension properties, but slow drying gave high compression moduli. This latter result may be due to more time for particle packing and compression during drying. The quantification of dust generation during a cutting event was difficult with a laboratory test method. Using the straight-edge cutting method, expected trends were documented: dust level increased with increasing coating weight and decreasing binder level. Dusting level decreased with increasing pigment shape factor. The rotary cutter method proved to be ineffective in producing repeatable results. The result is caused by the need to cut with conditions that duplicate the slitter geometry and to low amounts of dust generation. The low amount of dust is difficult to sensitively quantify with gravimetric methods