Paper and cardboard have a certain directionality after being formed by a paper machine. Generally speaking, paper is divided into two directions: the direction parallel to the running of the paper machine is longitudinal; the direction perpendicular to the running of the paper machine is transverse. Because the longitudinal and transverse properties of paper are different, many properties of paper are also different, such as tensile strength and folding strength, the longitudinal direction is greater than the transverse direction, and the tear is greater than the longitudinal direction. Many papers are used with machine direction and cross direction strengths as close as possible, but some papers require machine direction strength. Therefore, when determining the performance of paper, it is necessary to distinguish between landscape and portrait orientation.
The longitudinal and transverse directions of paper without creping treatment (including elastic treatment) shall be measured by one of the following methods.
(1) paper strip bending method
Take two paper strips with a length of 200 mm and a width of 15 mm perpendicular to each other parallel to the sides of the original sample. Overlap it and pinch one end with your fingers. Keep it horizontal and let the other end hang down freely. Such as two pieces of paper separated. Then the lower paper strip is bent greatly, which is the horizontal direction of the paper; if the two paper strips overlap, that is, the upper paper strip is pressed on the lower paper strip, and the two paper strips are not separated, then the upper paper strip is horizontal.
(2) Paper Curling Method
Cut a test piece of 50mm×50mm square or 50mm in diameter parallel to the edge of the original sample, and mark the direction corresponding to the edge of the original sample, then float the test piece on the water surface, when the test piece curls , the direction parallel to the curling axis is the longitudinal direction of the paper.
(3) Tensile strength identification method
According to the direction of the strength of the paper strip, cut two perpendicular paper strips with a length of 250 mm and a width of 15 mm parallel to the edge of the original sample, and measure its tensile strength. Generally, the one with the highest tensile strength is the longitudinal direction. For example, when determining the burst resistance of the test piece to distinguish the direction, the direction at right angles to the main line of rupture is the longitudinal direction.
(4) Fiber orientation identification method
According to the fiber arrangement direction of the paper surface, especially most of the fibers on the dull surface are identified along the longitudinal arrangement. When observing, the paper is placed flat, and the human light is at an angle of about 45" to the paper surface, and the line of sight is also at a 45° angle to the paper surface to observe the arrangement direction of the fibers on the paper surface. Observing the paper surface under a microscope is also helpful to identify the fiber arrangement direction.
Determination of the longitudinal and transverse directions of the paper with crepe treatment (including elastic treatment); the direction parallel to the wrinkles is the transverse direction of the paper.
