Longitudinal and horizontal judgment method of kraft paper

Kraft paper is divided into longitudinal and transverse directions. Most of the fibers are arranged in the direction of the running direction of the paper machine, and in this direction, the kraft paper bears a greater traction, which is the so-called machine direction. The cross direction of the kraft paper is perpendicular to the running direction of the paper machine.
When measuring various physical properties, the direction of the kraft paper must be considered. When measuring the tensile strength, folding endurance and tear resistance, two paper samples should be cut from the longitudinal and transverse directions to measure the strength in both directions. The tensile strength and folding resistance are larger in the longitudinal direction than in the transverse direction; the tearing force is larger in the transverse direction. When determining the optical properties of paper, such as whiteness and gloss, the orientation of the kraft paper must be considered.
There are several ways to determine the vertical and horizontal directions of kraft paper, which are explained as follows:
1. According to the vertical and horizontal directions of the kraft paper, cut into two paper patterns (6 by one-half inch), and observe the stiffness in these two directions. The stiffness of the tissue paper is large longitudinally and laterally, and can be measured with a stiffness meter. You can also hold two sheets of paper at the same time and hold one end in your hand, and pay attention to which one is more bent;
Second, use visual inspection. Most kraft papers can be seen to have more fibers aligned in the machine direction. The long side of the copper mesh is often parallel to the longitudinal direction;
3. Tear the thin paper made on the rotary screen machine in two directions, and observe the tearing direction; the vertical and horizontal directions of the kraft paper can be distinguished. Because the longitudinal tear resistance of kraft paper is small, the direction of tearing tends to be parallel to the longitudinal direction.
4. Determination of the tensile strength or folding endurance of the kraft paper in the longitudinal and transverse directions. Generally, the longitudinal direction has a larger tensile strength and folding resistance than the transverse direction;
5. When measuring the bursting strength, observe the rupture of the paper sheet. This observation is based on the fact that the longitudinal elongation of the kraft paper is smaller than the transverse direction. When testing the bursting strength, the kraft paper is subjected to the pressure of the rubber film of the bursting strength tester, and it is easy to elongate in the transverse direction, but cannot be significantly elongated in the longitudinal direction, and suddenly ruptures, so the direction of the longest crack is perpendicular to the longitudinal direction;
6. Wet the surface of a small square of paper pattern, and note that the curled axis is often parallel to the longitudinal direction. The reason for the curling is that the moisture makes the polar surface under the sheet elongated, because the kraft paper is elongated laterally than the longitudinal direction, which makes the sheet rolled into a cylinder, and its axis is parallel to the longitudinal direction;
The aspect ratio of kraft paper varies. The kraft paper produced by the rotary wire machine has a larger ratio of aspect ratio than the kraft paper produced by the longer wire machine. That is kraft paper made of fourdrinier wire machine, and the total longitudinal tensile strength is 1.5-2 times larger than that in the transverse direction. The back (reverse) of the Fourdrinier kraft paper, the longitudinal arrangement of the fibers, is very remarkable. On the top (front), it's not very noticeable. Adding the least amount of colored fibers to the stock, it was found that the number of fibers aligned longitudinally on the reverse side of the kraft paper was ten times the number of fibers aligned transversely.
On the front, unless it is very close to the longitudinal direction, the number of fibers arranged in the other directions is approximately equal. The number of fibers aligned parallel to the machine direction is twice as high in other directions. The results of fiber counts are expressed in polar coordinates. A straight line drawn from the center to any direction intersects the curve, and the length of this straight line represents the number of fibers arranged in this direction.
When making paper, the working condition of the paper machine has a very significant influence on the ratio of longitudinal and transverse strength. Its important factors generally include the relationship between the vibrating disc of the paper machine wire case, the pulp speed and the wire speed, and the size of the drafting force on the wet paper sheet also has a great influence.
Under normal circumstances, the changes in the longitudinal properties of kraft paper are less in the transverse direction, because the longitudinal changes are relatively slow, and due to uneven pulp flow on the wire, uneven wet pressing, or uneven stress during drying, it may occur very suddenly. Lateral changes. In addition, the strength of the kraft paper in the transverse direction also varies according to the distance between the sampling site and the edge of the paper.
Many kraft papers require machine and transverse strengths to be as close to the same as possible. However, there are exceptions, such as sometimes requiring maximum longitudinal tensile strength (such as cable paper and paper rope paper). All kinds of kraft paper should take advantage of the maximum advantage of its forward direction. For the cutting of printing paper, it is best to place the longitudinal A long side. When the kraft paper enters the printing press, the longitudinal direction is parallel to the axis of the embossing roller. Diazo type paper is also cut longitudinally.
Book paper In order to facilitate folding and opening of the book, the longitudinal direction is preferably the upper and lower directions of the pages of the book. When manufacturing chart card paper, it is best to cut the longitudinal direction of the kraft paper into the vertical direction of the chart to obtain the advantage of greater rigidity in this direction. When bonding multiple layers of kraft paper, it is sometimes expected that the longitudinal and transverse directions of each layer of kraft paper can be crossed. Although this is not always possible. Labels wrapped around the perimeter of metal cans are often cut into kraft paper longitudinally in the upright direction of the can to obtain maximum flexibility around the can.