Paper is divided into front and back. The side attached to the copper mesh is the reverse side, also known as the mesh side, and the side in contact with the blanket is the front side, also known as the blanket side . The back of the paper has texture, and the loss rate of fine fibers is large. Since this surface makes the surface of the paper rough and loose, the front side is relatively tight. Since the front and back of the paper are different, the difference in composition between the two sides of the paper makes certain properties of the paper (such as smoothness, whiteness, sizing, etc.) different. This difference is called the two-sidedness of the paper. Certain performance tests of paper are usually performed on both sides. If only one side is to be tested, you need to state which side is to be tested. Therefore, the front and back sides of the paper should be identified before inspection.
The identification method of the front and back of the paper is as follows.
(1) Intuitive method
Fold a test piece and observe the relative smoothness of one side. The wire surface is often recognizable from the diamond-shaped indentations of the papermaking wire. Hold it horizontally so that the incident light is at a 45° angle to the paper surface, and the line of sight is also at a 45° angle to the paper surface to observe the web marks on the paper surface. The paper surface can also be observed under a microscope to help identify the mesh surface.
(2) wet method
Before impregnating the paper with water or dilute sodium radon oxide solution, drain the excess liquid, let it stand for a few minutes, and observe both sides. If there is a clear screen printing, it is the reverse side.
(3) Tear method
Holding the test piece in one hand so that the longitudinal direction is parallel to the line of sight and level with the surface of the test piece, with the other hand pull the paper up so that it tears in the longitudinal direction first. Then gradually turn the direction of the tearing paper to the horizontal direction, and tear it to the outside of the paper. Turn over the paper so that the other side faces up, and still tear the paper according to the above method. Comparing the paper wool on the two tear lines, the hair on one line is more obvious than the other. Especially at the longitudinal, turning, and horizontal curves, the paper wool is obviously the mesh surface, and when the mesh surface is upward, the paper wool edge is even worse.
More than one of the three identification methods can be selected for identification.
