Q&A about printing paper (98-105)

98. What is the mechanical strength of paper?

A: The mechanical strength of paper is usually expressed in terms of the amount of stress that destroys the integrity of the paper and irreversibly changes the structure. According to the nature of the external forces acting on the paper, the mechanical strength of the paper is often expressed by different indexes such as tensile strength, folding resistance, and tearing degree.

In practical applications, whether the paper is prone to break, break or tear paper diseases, is not determined by one or several of the above strength indicators, but also with the paper's elongation, rigidity, brittleness and the corresponding dispersion capacity Comprehensive factors are closely related. Therefore, a comprehensive analysis and understanding of the paper's mechanical properties should be made from the paper's strength indicators and other related performance.

99. What is the tensile strength of paper?

A: Tensile strength is the maximum tensile force that a unit width of paper or paperboard can withstand before it breaks under the conditions specified in the standard test method. Tensile strength is generally expressed as the tensile value measured on a tensile strength tester divided by the width of the sample in kilonewtons per meter (kN/m).

Due to the different quantification of paper, its thickness is also different. The tensile strength ignores the difference between thick paper and thin paper. It only reflects the maximum tensile force per unit width, and does not reflect the “texture” strength of the paper, ie the unit cross-sectional area. The tensile strength. Therefore, the index indicating the tensile strength is usually the fracture length and the tensile index.

100. What is absolute tension?

A: Absolute resistance refers to the width of the sample specified by the paper or paperboard standard. The load F, read directly on the tensile tester, is measured with N.

101. What is the split length?

A: The split length is a hypothetical strength concept. It means that the length of a paper strip breaks when it cannot withstand its own weight. It has nothing to do with its thickness. It is suitable for comparing the tensile strength of different kinds of paper or board. Calculated as follows:

L--broken length (m);

B--sample width (m);

F - tensile strength of the specimen (N);

W - Quantitative sample (g/m2).

102. What is the tensile index?

A: The tensile index is the tensile strength of a paper based on the unit width and the tensile strength of a specific sample. The formula is as follows:

X--tensile index;

F--Stress (N);

W - Quantitative sample (g/m2);

W0--100g/m2;

B--sample width (1.5cm);

B0--1.0cm.

103. What is the elongation of the paper?

Answer: When the paper is stretched under tension, it will stretch in the direction of force. When the tension is increased so that the strip is broken, it stretches to its limit. The ratio of the elongation of the paper or paperboard to the breakage from the tension to the original length is the elongation of the paper, and the elongation can be measured at the same time as measuring the tensile strength of the paper.

104. How to improve the tensile strength of paper?

A: The tensile strength of paper depends mainly on the binding force between the fibers and the strength of the fiber itself. Therefore, choosing the type of papermaking pulp and a good beating process is the key to achieving higher tensile strength. In addition, adding an appropriate amount of reinforcing agent will also greatly improve the tensile strength of the paper.

105. What are the requirements for printing paper against tensile strength?

A: The tensile strength and elongation of paper are very important indicators for newsprint, offset book, and especially for high-speed web presses. The paper on the high-speed rotary press is in a state of uniform tension during the entire printing process, and the paper is subjected to a certain pulling force in the longitudinal direction. If the tensile strength of the paper is lower than this pulling force, paper breakage may occur. Therefore, there is generally a certain requirement for the tensile strength of paper. The increase in elongation can promote and improve the internal stress distribution of the paper, reduce the stress concentration, buffer the fluctuating tension on the paper strip, and prevent and reduce the paper surface breakage.

- "Printing Technology - Equipment and Special Printing"