length, this property is important Because it has a decisive influence on the behaviour of the paper web during its high-speed processing (e.g. during the coating process on individual sections of the coater). A desirable feature for coated paper is the tensile force at break parameter as high as possible. The lower the value of the paper tensile force at break, the greater the probability of a break during the operation of a drying process or a coated web winding operation. The uncoated backing paper had an initial tensile force at break of 155.6 N. This parameter for the coated samples was in the range of 136.4 ÷ 183.0 N. Similarly to the width related force with break, the coatings applied with some Mayer rods caused a decrease in the tensile force at break of the paper to 12% (rods no. 4 - 7) or an increase of the parameter value by 3 ÷ 18% (rod s no. 8 - 15) (Tab. 2). The strain at break of paper ( H T ), defined as a measure of deformation under tensile stress, up to the point where the paper sample breaks, significantly affects the behaviour of coated paper under production conditions paper. The initial strain at break for the base paper prior to the coating process was 2.53%. Coating the samples, regardless of the thickness of the applied coating, increased the stretchability o f the paper by 6 ÷ 14% (Tab. 2). The consensus between tensile force at break and strain at break is the energy absorption parameter ( W T b ). The energy absorption describes the resistance of the test paper to the dynamic load acting on it. The higher the values of the energy absorption the tested paper achieves, the more resistant it is to the dynamic loads acting on it. The initial value of the energy absorption for the base paper before the coating process was 245.4 J/ m². On the basis of obtained results, it can be observed that only the use of the lowest number rod resulted in a slight decrease in the parameter. The remaining samples coated with rods no. 5 - 15, were characterized by higher values of the energy absorption by 2 ÷ 31% (Tab. 2). The increase in the value of the energy absorption with the increase of the coating grammage was also observed. Taking into account different weights of coatings, the analysis of the energy absorption of the samples was extended to include the energy absorption index, i.e. the work necessary to break the tested paper sample with respect to its weight. The initial value of the considered parameter for the base paper before the coating process was 1.96 J/g. The analysis of the results showed an increase in the energy absorption index for the samples with the highest grammage of the coating by 9 ÷ 22%. The samples with lower coating thicknesses (coated with rods no. 4 - 8) showed the decrease of the considered parameter not exceeding 9% (Tab. 2). For the analyzed samples, the tensile stiffness, i.e. the resistance of the paper samples to deformations caused by external tensile forces, was also determined. The initial value of the tensile stiffness for the base paper was 1,290 kN/m, while for the coated samples it was within the range of 1,098 ÷ 1,438 kN/ m (Tab. 2). Depending on the Mayer rod used, the application of the coating compound to the paper resulted in a decrease or increase in the parameter value. It was also observed that with the increase of the coating grammage, the tensile stiffness of the sample increased. In the case of the tensile stiffness index, a decrease in the parameter was observed for most of the tested samples by 6 ÷ 18%. Only for the papers with the highest grammage of the coating, coated with rods no. 12 and 15, a very slight increase in the value of the considered parameter was observed (Tab. 2). The last parameter tested for papers coated with various mixtures was Young's modulus of elasticity. This parameter characterizes the ability to distribute stresses acting on the material and describes the ability of an elastic body to resist deformation when stretched. The lower the value of Young's modulus, the better the tested paper has the ability to distribute stresses acting on it.
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