Paper is the most commonly used material for packaging and printing. Its physical properties will have a direct or indirect impact on the quality of printing. Correctly understanding and mastering the nature of paper, according to the characteristics of the product, the rational use of paper to improve the product's printing quality, will play a positive role in promoting. 1. Quantitative. It refers to the weight per unit area of ​​the paper, expressed in g/m2, which is the weight of one square meter format paper. The level of paper quantification determines the physical properties of the paper, such as tensile strength, tear strength, tightness, stiffness, and thickness. This is also the main reason why high-speed printing presses do not print well on paper with a basis weight of 35 g/m2 or less. This may cause unsustainable continuous papers, inaccurate overprinting, and other reasons. Therefore, according to the characteristics of equipment, prints corresponding to their quantitative properties are arranged for production. In order to better reduce consumption, improve product quality and equipment printing efficiency. 2. thickness. It is the thickness of the paper, the unit of measurement is usually expressed in μm or mm. Thickness is closely related to the quantitative and tightness. In general, the thickness of the paper is large and its quantification is correspondingly high, but the relationship between the two is not absolute. Some papers are thin, but their quantification is equal to or greater than that of thicker ones. This shows that the degree of tightness of the fibrous structure of the paper determines the basis weight and thickness of the paper. From the perspective of printing and packaging quality, it is very important that the paper thickness is uniform. Otherwise, it will affect the auto-feed, printing pressure and ink quality. If a book is printed on different thicknesses of paper, there will be a noticeable difference in the thickness of the finished book. 3. Tightness. It refers to the weight per cubic centimeter of paper, expressed in g/Cm2. The tightness of the paper is calculated from the basis weight and thickness according to the following formula: D = G/d × 1000, where: G represents the basis weight of the paper and d is the thickness of the paper. Tightness is the degree of measuring the density of the paper structure. If the degree of tightness is too large, the paper will be brittle, the opacity and ink absorption will be significantly reduced, the imprinting will not be easy to dry, and the phenomenon of sticky and dirty bottom will easily occur. Therefore, the tightness of the paper printing should pay attention to a reasonable grasp of the control of the amount of coating ink, and select the corresponding dry ink. 4. hardness. It is the performance of paper that resists the indentation of another object, and it is also the rough appearance of paper fibrous tissue. Paper hardness is low and clearer prints can be obtained. The letterpress printing process is generally more suitable for printing with a paper with a low hardness, so that the printing ink is of good quality and the printing plate has a high printing rate. 5. Smoothness. It refers to the degree of surface roughness of the paper, expressed in seconds and measurable. The detection principle is: the time it takes for a certain volume of air to pass through the gap between the surface of the glass plate and the surface of the sample under a certain degree of vacuum and pressure. The smoother the paper surface, the slower the speed at which the air passes, and vice versa, the faster the air passes through. Printing requires a moderate degree of smoothness, a high degree of smoothness, and faithful reproduction of fine dots, but care should be taken to prevent the back of the print from becoming dirty. If the smoothness of the paper is low, the required printing pressure is large and the ink consumption is also large. 6. Degree of dust. It refers to the impurity spots on the paper, and there is a clear difference between the color and the paper color. The degree of dust is an index for measuring the amount of paper surface impurities, and is expressed as the number of dust areas within a certain range on a paper surface per square meter area. The degree of paper dust is high, and the ink and the dot reproduction effect of the printed product are poor. Dirty spots affect the appearance of the product. 7. Sizing degree. The paper surface of writing paper, coated paper, and wrapper are generally sized to form a water-resistant protective layer. How is the sizing degree used, and in a few seconds, a standard ink specially prepared by the duck pen and paper draws a line on the paper surface to see the maximum width of non-diffusion and impermeability, and the unit is mm. The degree of paper sizing is high, the brightness of the printed ink layer is also high, and the ink consumption is small. 8. Ink absorption. It is the ability of the paper to absorb ink. Paper with good smoothness and sizing degree has weak ink absorption, and the ink layer dries slowly, and it is easy to stick dirty prints. On the contrary, ink absorption is strong and the printed products are easy to dry. 9. Vertical and horizontal. It refers to the direction in which the paper fibers are arranged. In the process of papermaking, the fiber is running in the direction of the paper machine along the longitudinal direction of the paper. It can be identified from the sharp corners of the web marks. Longitudinal to the longitudinal direction is the horizontal direction, the vertical paper pattern printing deformation value is small, the horizontal paper pattern printing process has a larger amount of stretching and variation, and the tensile strength and the tearing degree are all poor. 10. Expansion rate. It refers to the dimensional variation that occurs when the paper absorbs moisture or water is lost. The softer the fibrous structure of the paper, the lower the tightness, the higher the paper's stretch rate; conversely, the lower the stretch rate. In addition, papers with good smoothness and sizing degree have a low expansion rate. Such as double-sided coated paper, glass cards and A and other offset paper. 11. Air permeability. In general, the thinner the paper and the lower the tightness, the greater the air permeability. The unit of air permeability is ml/min (ml/min) or s/100 ml (second/100 ml), which means the amount of air that passes through the paper in one minute or the time required to permeate 100 ml of air. Paper with high air permeability is prone to attract double paper during the printing process. 12. BaiDu. It refers to the brightness of the paper. If the paper reflects all the light, it can be seen by the naked eye as white. To measure the whiteness of paper, the whiteness of magnesia is usually defined as 100% as a standard, and the paper sample is irradiated with blue light, and the whiteness of the small reflectance is poor. Optical whiteness meter can also be used to measure whiteness. The unit of whiteness is 11%. Paper with high whiteness appears dark in printing ink and is prone to print-through phenomena. 13. Positive and negative. In papermaking, the pulp is attached to a stencil and set in a filtered, dehydrated manner. In this way, if one side of the net is lost due to fine fibers and fillers with water, net marks are left and the paper surface is thicker. The other side is less dense without relying on the net. Smooth, so that the paper forms a positive and negative surface difference, although the production has been dried, calendered, there are still differences on the positive and negative. The positive and negative gloss of the paper is different, which directly affects the ink absorption performance and the printing quality of the product. If the letterpress process uses a thicker paper print on the reverse side, the plate wear will be significantly increased. The paper's frontal printing pressure is light and the ink consumption is also low. To sum up, correctly understand and identify the main physical properties of paper and its impact on printing, according to the nature and characteristics of paper, take appropriate measures from the operation, process technology, to avoid blindness in production, can effectively Reduce or prevent the occurrence of printing failures, thereby ensuring production efficiency and product print quality.
Understand Different Paper Properties to Improve Packaging Print Quality