As we all know, two-sidedness is a very important parameter to control in paper making. Paper two-sidedness has a great influence on many aspects of the whole process of printing, such as dot gain, print density, ink absorption, and so on. If the value of two-sidedness is too high or too low, it will cause print quality problems. So how does two-sidedness affect printing quality?
What is two-sidedness?
The first thing we need to know is: What is two-sidedness? There are two sides to everything, including paper. On one side, there is a smooth and soft surface whereas on the other side is a rough and textured surface. Two-sidedness, also called D/S value or air permeability, refers to the ratio of the speed of the air passing through a given sample to the speed of an equal volume of air passing through a standard sample. The unit is m/s.
The D/S value of the paper is an important parameter to control the smoothness of the paper surface and the evenness of the porous structure. It reflects the porosity of paper and has a great influence on printability, such as print density, ink absorption, and dot gain.
Generally speaking, the two-sidedness of coated paper is lower than that of uncoated paper, and the two-sidedness of high-quality coated paper is lower than that of ordinary coated paper. The two-sidedness of cast-coated paper is the lowest.
Impact of two-sidedness
The main reason for the poor print quality of high two-sidedness paper is that the ink absorption is too fast, which leads to difficulty in controlling the printing density and dot gain, and even the phenomenon of offset printing.
In addition, when the two-sidedness of the paper is too high or too low, it will also cause poor print quality. If the two-sidedness of the paper is too high, the ink will spread on the paper surface, which will cause the printing density to be low and the color to be light; if the two-sidedness of the paper is too low, the ink will not be able to penetrate into the paper in time, which will cause poor printability.
Two-Sidedness problems in Printing Quality
Different origins of wood pulp fibers make the surface characteristics and internal structure of paper two sides not exactly the same; In the process of making paper, one side or both sides of the paper are usually calendered, and the degree of surface smoothness is not exactly same; Paper two sides have different air permeability, so the paper two sides also absorb and release ink in a different way.
The paper’s two-sidedness will cause the printing ink to penetrate into the paper too slowly or quickly, resulting in printing registration accuracy and color difference. If the ink acceptance is low, it will cause poor adhesion between the ink layer and the paper surface, which leads to color fading; if it is high, it will lead to ink penetration, that is, color mixing. In addition, the two-sidedness of paper can also cause web tension differences and web guide accuracy problems in high-speed printing, which will seriously affect the registration accuracy and image quality of printed products.
How to solve the problem of two-sidedness
The two-sidedness of paper is an important factor affecting the printing quality. In paper making process the main reasons for the two-sidedness of paper are pulping process, screening process, Dehydration. So how to solve the problem of two-sidedness? There are many ways to solve paper two-sidedness problems.
In order to solve the problem of paper two-sidedness, it is necessary to improve the surface strength and smoothness of the paper by adding a certain amount of surfactant in the papermaking process, so as to make the ink layer adhere more firmly to the surface of the paper and prevent color fading. In addition, we can also use offline calendering or online calendering technology to improve the surface smoothness of the paper and make it more suitable for high-speed printing.
Dehydration is another important factor affecting the two-sidedness of paper. To reduce this factor we can use vertical twin-wire in forming the section. Here two-side dehydration occurs at the same time, so paper two side’s performance can be closer.
We can also reduce two-sidedness effects by using a variety of printing methods and papers, so that the ink on both sides can be evenly absorbed;
With the development of science and technology, more and more effective methods will be used to solve paper two-sidedness problems. So we believe that in the near future, all paper two-sidedness problems can be solved perfectly.
Conclusion
Paper two-sidedness is a common problem in paper making, and it has a great impact on printing quality. As we can see from the above, there are several ways to solve paper two-sidedness. Paper manufacturers can choose appropriate methods according to their own production conditions and paper qualities. In addition, it is also necessary to do a good job in paper-making process control and equipment maintenance, so as to ensure the stability of paper two-sidedness and improve the printing quality of paper products.
