Printability and Variable Factors of Paper (I)

The printability of paper usually refers to the adaptation or reaction characteristics of the paper when it is printed, subjective to a large extent, and subject to different standards. For example, most papers can be printed with most printing processes from a technical point of view, but this will not work from a commercial or economic point of view. Similarly, when judging the quality of a printed matter, the characteristics of the printed matter must be considered. For example, the judging criteria for a quality flexo-folding carton is different from the quality judgment standard for a student's exercise book.
Furthermore, it must be clear that the quality of printing depends on the combined effects of paper, ink, printing plates, anilox rollers, and printing presses, and of course on the preparation and operation of the press. If there are mistakes in other areas, even a well-printed paper will not achieve satisfactory print quality. The term printability is used to describe many physical and chemical properties of paper, which restrict the production of prints, commercial batch printing and expected quality, and printing speed. In the following pages, this article will focus on some of the characteristics of paper (including paperboard, translator's note) itself, ink and the impact of printing plates on the printability of paper.
There are many types of paper used in flexible packaging, prepress and postpress, such as coated paper, semi-coated paper, uncoated paper and Kraft paperboard. Paper with good printability only absorbs the proper amount of ink at a predetermined location and does not affect its normal drying process. In addition, the paper should also have a certain degree of smoothness, ink penetration, suitable optical density and rheological properties (compressibility and elasticity). The paper should also have sufficient surface strength to prevent fuzzing; the shape and size should be stable and not subject to change in wetness. The surface of the paper should not have adhered dust particles and it is not easy to generate or maintain static electricity.
When it comes to the printability of paper, we must consider the situation when the ink comes in contact with the paper. This involves the momentary printing pressure on the paper. After the paper is pressed, the smoothness is further improved, and at the same time, the pores on the surface of the paper are reduced. The compressibility of the paper plays a role, making the surface easily wet with ink, which is beneficial to ink absorption. In an ideal situation, the paper should be restored to its original shape after being pressed, especially those papers that have only been subjected to rough calendering.
Ink transfer ink transfer is characterized by ink absorption. But this statement is not precise enough, because it contains this meaning: paper inhales a lot of ink. Actually it does not need that, it will consume excess ink. Therefore, the term "inking performance" is widely used now, and its meaning is also relatively precise. Due to the difference in ink, paper, and smoothness, the pore size of the paper is not the same, so the amount of ink seepage is not the same under a certain printing pressure.
In fact, as long as the specified minimum ink transfer amount is sufficient, it can ensure the formation of the required ink film and quality, so that the ink is transferred to the surface of the paper as much as possible and firmly adheres to the surface of the paper. Does not cause stickiness. In order to obtain a good ink hiding power, the binder (liquid phase) in the ink must penetrate the pores on the surface of the paper to allow the pigment to adhere to the surface of the paper. Smooth paper can achieve higher ink hiding power, while rough paper requires more ink to get the desired effect. Rough paper also tends to cause larger dot gain than smooth paper. This is related to paper type, paper surface roughness, and pore size. As long as you compare the outlets on the printed sheets with those on the plates or on the film, you can see how much the outlets increase. The densitometer is usually used to find the dot value, and then the dot value is marked on the graph. Each color curve plotted reflects the printing performance of the press, paper, printing plates, and inks used, providing us with an important stopover for dot gain and tone reproduction, using specific inks, plates, and paper in printing. The data obtained after on-press printing has a very important guiding role for the flexo printing and color separation.
Of course, the binder and the pigment should not be separated where the ink adheres to the surface of the paper, which cannot be ignored. In addition, overprinting has a great influence on printability. In order to obtain a good overprint effect, the pH value of the water-based ink should be valued. The pH of the ink used for the first ink should be between 9-9.3. The pH of the ink used for the first ink should not fall below 9. The pH of the ink used for the second ink should be lower. The dryness of colored overprinting inks is generally light-colored and dark-colored (yellow-product line-blue). When printing on coated or semi-coated paper, the color sequence is sometimes changed to magenta-yellow-cyan in order to achieve a better overprinting effect for water-based inks. (To be continued)