Optimizing printability makes the quality of corrugated board printing process greatly improved (1)

The term printability is a subjective judgment of the printing process. It usually means that the paper responds to the printing process in some way, and it needs to adjust the reaction to meet the production requirements through some standards. For example, from a technical point of view, printing on a variety of papers can be achieved by most printing methods, but from a commercial or economic point of view, this process may not be feasible. Therefore, the evaluation of high-quality prints should take into account its main characteristics. For example, printing a high-quality packaging carton by flexographic printing is completely different from printing some exercise books with only a few lines. The choice of the person's printing method should take the clarity of the line as the focus of consideration. In addition, print should also be seen as the result of the interaction between paper, ink, plates, metal rollers, printing presses, and how to prepare for printing and handling. Even if the paper has good printability, if other relevant factors are not suitable, no high-quality prints can be printed. The definition for printability is the physical and chemical properties of the paper, which control the yield, quality, and output rate of the print. This article mainly describes the effect of paper base, ink, and printing plate on the printability of paper products that require post-processing of corrugated paper.

Paper base Many types of paper, such as coated paper, semi-coated paper and non-coated paper, kraft paperboard, or test paperboard, can be used for preprinting or postpress printing. Paper with good printability will absorb the proper amount of ink in place and will not negatively affect its dryness. The paper can also exhibit desirable print smoothness, ink permeability, proper optical density and good rheology (compressibility and elasticity). It should also have sufficient surface tension to prevent lint or lint, and it should also have good dimensional stability to avoid severe deformation in humid air. The surface of the paper should not be separated from the particles, and the generation of static electricity will not have negative consequences for the printing process.

The concept of printability makes us inevitably consider what happens when paper and ink meet in extremely short time and under extremely great pressure. The pressure exerted on the paper significantly improves the smoothness of the paper and reduces the pore size of the surface. The size of the pressure and the ease with which the ink wets the surface of the paper are very important, especially for papers with rough surfaces.

The smoothness of a smooth paper can affect the color uniformity of the print, the appearance of the ink layer and the overall print. There are two ways to describe smoothness defects, both macroscopic and microscopic. Macroscopic defects are irregular changes that can be noticeable to the naked eye, such as severe changes in thickness or wrinkling, sometimes caused by the irregular shape of the fibers. Microscopic defects refer to flaws that are invisible to the naked eye, such as tiny pits or holes, which can cause the loss of dots and degrade the quality of printed products.

Another printability problem with paper dust is the deposition of fine particles falling off the surface of the paper into the ink or the surface of the drum. If no filter device is installed in the ink supply system on the flexographic printing press, these small particles may accumulate and transfer to the plate. This phenomenon is often referred to as dirty plate. One way to solve this problem is to Install the ink filter in front of the ink pump so that these dirty particles may be intercepted by the auxiliary blade. Paper scraps will greatly reduce the ink's suitability for paper.

The color of the visual effect paper and the ink film formed after the ink is fixed on the paper are also very important. Obviously, the color of the paper will have an effect on the visual effect, so the visual effect produced by printing the paper with different colors on the paper immediately using the same ink is different. In addition, the use of different types of paper for the same job can also result in inconsistent print quality.

Chemical Factors The chemical composition of paper can strongly affect the printability. Too much acid may prolong the drying time of ink, which is especially important in tropical countries and areas with high humidity. Because the moisture contained in the paper is relatively high, the drying speed is also more demanding. high. Usually coated paper with a pH between 5 and 5.5 and coated paper between 7 and 8.5 should ensure effective ink drying unless the ambient humidity is too high, such as when the humidity exceeds 65%, it is not always possible. Guarantee effective drying. Maintaining consistency in the humidity of the working environment is very important for obtaining high quality prints. If the humidity of the environment is too high, the paper will constantly absorb water molecules like a sponge, and generally want to make the paper reach a state of equilibrium, that is, the paper will neither absorb moisture nor release moisture. Different grammage papers have different equilibrium points. For example, a dense white paperboard may have an absolute humidity of 6%. In the same environment, unbleached kraft paperboard may have a 7.5% humidity value. The normal moisture standard is 5% to 7%. Exceeding this value will change the ink absorbency and add an extra burden to the drying system.

However, the low moisture content of the paper may cause the ink to crack when the final print is folded into a box, because the paper absorbs the excessive pressure caused by the expansion of moisture in the air to the ink layer.