the estimate the usable properties of many products. This is particularly important for the evaluation of the usefulness of packaging and newsprint papers. Figure 3 shows a comparison of the breaking length of papers with different thicknesses of the coating. The initial value of the breaking point for the base paper before the coating process was 12 650 m. In the grounds on the presented results (Fig. 3), it can be observed that the coating process using most of the Mayer rods used (No. 4 - 9) caused a decrease in the value of the breaking length of the paper by 1 ÷ 14%. Only two samples with the highest coating weight increased the parameter value by an average of 6%. On this basis, it can be concluded that the breaking length capacity of the coated paper decreases to a certain coating thickness. Only a relatively high development in the coating grammage causes an increase in the tear resistance properties.
14000
13500
13000
12500
12000
11500
11000
10500
3 4 5 6 7 8 9 10111213141516 Mayer Rod Number
Figure 3. Influence of coating grammage on the breaking length of paper Another analyzed index characterizing the functional properties of coated paper samples was the width related force with break ( V T b ), is one of the basic static strength properties and determines the value of the breaking load causing a 1 m wide sample of a paper to break. The value of the V T b for the base paper before the coating process was 15 490 N/m, while after coating it was within the range of 13 700 ÷ 18 570 N /m. Interestingly, applying the coating with some Mayer rods resulted in a decrease in the parameter b y 4 ÷ 12% (rods No. 4 - 7), or its increase to 20% (rods No. 8 - 15). Regardless of that, the increase in the coating grammage caused a commensurate increase in the width related force with break (Tab. 2). The force at break index ( V T W ) was also determined, i.e. the value of the width related force with break that a hypothetical 1 g/ m² paper sample would achieve. The force at break index is an extremely practical parameter because it allows to carry out free and reliable comparison of coated paper samples, both for a wide range of base papers of different weights and for paper with coatings of different weights. Therefore, the presented property allows the coated sample of the paper to be assessed in terms of its material properties. The base paper used for the coating process had an initial value of the force at break index at the level of 123.8 N/mg, while the coated samples were 105.9 ÷ 133.2 N/ mg. Thus, depending on the grammage of the coating, an increase or decrease of the considered parameter was observed (Tab. 2). The same characteristics of the test specimen as the width related force with break represent the tensile force at break ( F B ). This parameter is also one of the basic static properties that characterize the performance of paper products. It specifies the limit value of the stress which, if exceeded, will break the tested sample of the coated paper. As in the case of breaking
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