Understand different paper characteristics to improve the quality of packaging printing
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Paper is the most commonly used material for packaging printing, and its physical properties will have a direct or indirect impact on print quality. Correct understanding and mastery of the nature of paper, according to the characteristics of the product, the rational use of paper will improve the printing quality of the product, will play a positive role in promoting.
1. Quantitative. It refers to the weight per unit area of paper, expressed in g/m2, which is the weight of 1 square meter of paper. The degree of paper quantification determines the physical properties of the paper, such as tensile strength, tear, tightness, stiffness and thickness. This is also the main reason why high-speed printing presses are not good for printing papers of 35g/m2 or less, so that it is prone to abnormal paper feeding and inaccurate overprinting. Therefore, according to the characteristics of the equipment, the printing of the corresponding printing materials is arranged according to the characteristics of the equipment. In order to better reduce consumption, improve product quality and printing efficiency of equipment.
2. thickness. It is the thickness of the paper, and the unit of measurement is usually expressed in μm or mm. Thickness has a close relationship with quantitative and tightness. Generally speaking, the thickness of paper is large, and its quantitative correspondingly is high, but the relationship between the two is not absolute. Some papers are thin, but they are equal or thicker than thicker ones. This indicates the degree of tightness of the fiber structure of the paper, which determines the basis weight and thickness of the paper. From the point of view of printing and packaging quality, it is very important that the paper thickness is uniform. Otherwise, it will affect the automatic paper feed, printing pressure and ink quality. If you use a thin paper with different thicknesses, it will make the finished book produce a significant difference in thickness.
3. Tightness. It refers to the weight of paper per cubic centimeter, expressed in g/cm2. The tightness of the paper is calculated from the basis weight and the thickness according to the following formula: D = G / d × 1000, where: G represents the basis weight of the paper; d is the thickness of the paper. Tightness is a measure of the density of the paper structure. If the tightness is too large, the paper will be brittle, the opacity and ink absorption will be significantly reduced, the print will not be dry, and the sticky bottom will easily occur. Therefore, when printing on tight paper, care should be taken to control the amount of ink applied and to select the ink with the corresponding drying property.
4. hardness. It is the performance of the paper against the indentation of another object, and it is also the rough performance of paper fiber tissue. The paper has a low hardness and a clearer print is obtained. The letterpress printing process is generally suitable for printing on paper with low hardness, so that the quality of the printed ink is good, and the printing durability of the printing plate is also high.
5. Smoothness. It refers to the degree of unevenness on the surface of the paper, expressed in seconds, measurable. The detection principle is: the time taken 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, the slower the air passes, and vice versa. Printing requires paper with moderate smoothness, high smoothness, and small dots will faithfully reproduce, but the full version should be printed to prevent the back from being dirty. If the smoothness of the paper is low, the required printing pressure is large, and the ink consumption is also large.
6. Dust. It refers to the impurity spots on the paper, and there is a significant difference between the color and the paper color. Dustiness is an indicator of paper surface impurities, expressed as the number of dust areas in a certain range on a paper surface per square meter. The paper has a high degree of dust, and the printing ink color and dot reproduction effect are poor, and the dirty spots affect the appearance of the product.
7. Sizing degree. The paper surface of writing paper, coated paper and wrapping paper is usually formed by sizing to form a protective layer having water resistance. How to apply the glue, the standard ink specially made by the duck pen is used to draw a line on the paper in a few seconds to see the maximum width of the non-diffusion and impermeability, the unit is mm. The degree of sizing on the paper 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. For smoothness and good sizing, the ink absorption is weak, the ink layer is dry slowly, and the printed matter is easily adhered. On the contrary, the ink absorption is strong, and the printed product is easy to dry.
9. Vertical and horizontal. It refers to the direction in which the fibrous tissue of the paper is aligned. In the papermaking process, the fiber runs along the direction of the paper machine in the longitudinal direction of the paper. It can be identified from the sharp angles presented by the mesh marks. Vertically perpendicular to the longitudinal direction, the longitudinal paper grain printing deformation value is small, the lateral paper grain printing process has a large amount of stretching variation, and the tensile strength and the tearing degree are both poor.
10. Scaling rate. It refers to the dimensional variation that occurs when paper is lost after moisture absorption or water dispersion. The softer the fiber structure of the paper, the lower the tightness, the higher the stretch ratio of the paper; on the contrary, the lower the stretch ratio. In addition, paper having a smoothness and a good sizing degree has a small expansion ratio. Such as double-sided coated paper, glass card and A and other offset paper.
11. Breathability. In general, the thinner the paper, the lower the tightness, the greater the breathability. The unit of air permeability is ml/min (ml/min) or s/100 ml (sec/100 ml), which means the amount of air passing through the paper in 1 minute or the time required to pass 100 ml of air. Paper with high air permeability is easy to attract double paper during printing.
12. BaiDu. It refers to the brightness of the paper. If all the light reflected from the paper is visible, it will be white on the naked eye. The whiteness of the paper is measured. Usually, the whiteness of the magnesium oxide is set to 100% as a standard, and the paper is exposed to blue light, and the whiteness of the reflectance is small. Whiteness can also be measured using a photoelectric white meter instrument. The unit of whiteness is 11%. Paper with a high degree of whiteness, the printing ink is dark, and it is easy to produce offset.
13. Front and back. During papermaking, the pulp adheres to the steel mesh to be shaped by filtration and dewatering. In this way, if one side of the net is lost with water due to fine fibers and filler, the web marks are left and the paper surface is thick. The other side is not finer than the net. Smooth, so that the paper forms a positive and negative surface difference, although drying and calendering in production, there are still differences between the front and the back. The gloss of the front and back of the paper is different, which directly affects the absorption performance of the ink and the printing quality of the product. If the letterpress process uses a thicker reverse paper printing, the plate wear will be significantly increased. The front side of the paper has a light printing pressure and a low ink consumption. In summary, correctly understand and identify the main physical properties of paper and its impact on printing, according to the nature and characteristics of the paper, take appropriate measures from the operation and process technology to avoid blindness in production, in order to effectively Reduce or avoid the chance of printing failures, thus ensuring production efficiency and product printing quality.