prints with a greater degree of accuracy and sharpness. The practical conclusion is that only onigh-smoothness papers it is possible to accurately print an image with a high screen ruling.
Table 1. Structural properties of paper Mayer Rod number
Roughness
Air permeability
ml/min
ml/min
272 (15) 230 (21) 295 (11) 213 (16) 180 (10) 183 (13) 176 (8) 149 (11)
80 (7) 68 (4) 47 (4) 20 (3) 12 (4) 11 (4) 7 (2) 7 (2)
4
5
6
7
8
9
12
15
Note: Extended deviations are given in brackets. The thickness of the coating significantly influenced another, extremely important structural property of the paper, which is air permeability. The high air permeability is a desirable property in dustproof cartons and filter papers. However, many wrapping papers, especially food packaging paper should have a very low air permeability. On the basis presented results, it can be observed that the coating process with the use of the coating mixture significantly influences the structure of the tested base paper. Due to the fact that air permeability depends on the porosity and density of the article structure, an increase in the thickness of the coating caused a decrease in air permeability. The starting value of the parameter for the base paper before the coating process was 202 ml/min. The coated paper samples were characterized by air permeability within the range of 7 ÷ 80 ml/min, which is as much as 97 ÷ 60% lower. Theref ore, the change of the Mayer rod number by several numbers caused in this case significant differences in the value of the considered parameter. The level of air permeability indicates not only the porosity of the product but also other properties of the paper, including strength properties. The results of testing the strength parameters of the coated papers are presented in Table 2. It should be emphasized that the presented results were determined for the machine direction (MD). The strength parameters for this direction are of real practical value because in this direction the processing processes are carried out. Te mesurement of breaking length of paper is one of the most popular methods recommended for comparing the static strength properties of the tested papers. The parameter is generally used in the paper trade to describe the inherent strength of paper. Futhemore it constitutes a very good basis for comparing the strength of papers made from different materials and of different basis weight.The breaking length is a widely used indicator because it allows
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