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100 suggestions on rationalization of printing quality

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100 suggestions on rationalization of printing quality

high quality color image reproduction requires sufficient dynamic range and accurate control of image tone, neutral gray balance, granularity, color gamut range, detail and definition, which requires improving the recording resolution of inkjet printhead. The fundamental to solve this problem is to reduce the recording point size of inkjet printing. After the ink droplets are sprayed onto the surface of printing materials such as paper, they will dissipate the residual kinetic energy hitting the paper in the form of expanding on the surface of printing materials and penetrating into the interior of printing materials. Only after the expansion and penetration process is completed, the ink droplets will be converted into recording points. From this process, it can be seen that there is a causal relationship between the volume of jet ink droplets and the size of recording points on the surface of printing materials, so reducing the size of recording points means reducing the size of jet ink droplets. At present, the ink drop size of the nozzle used for fine image printing has been reduced to 3.5 picolin (PL, 1 picolin = 10-12 liters), and the ink drop size of the nozzle used for outdoor inkjet printing and packaging printing is between 9 and 50 pl. for example, the ink drop size marked in HP’s product manual is 42 pl
recording resolution and gray level
recording resolution refers to the number of points that can be printed by the inkjet equipment within the unit distance of the printing material. Generally speaking, the higher the recording resolution, the smaller and denser the recording points of ink drop conversion, and the finer the printing effect. However, the above conclusion is only applicable to binary inkjet technology, that is, printing can only be completed by spraying or not spraying ink droplets. Now most digital nozzles support multi gray level printing based on the principle of density modulation. Multi gray level printing refers to the printing technology that changes the density of recording points through the change of ink drop size under the same recording resolution, so as to produce different tones. The results show that the visual effective resolution is approximately equal to the product of the recording resolution and the square root of the gray level of the recording point. For example, the combination of 360dpi recording resolution and 16 gray levels can produce a visual effect equivalent to 1400dpi binary printing. Many commercial inkjet devices on the market support multi gray level printing. For example, hpscitex 11000 can spray ink droplets of 15pl, 30pl and 45pl through HP Scitex high dynamic range printing technology. By dynamically controlling the size of ink droplets, each recording point can form a density of 16 gray levels at most, so as to realize smooth transition color printing effect and fine image details
matching between substrate and ink
the surface characteristics and porous nature of paper determine the expansion and penetration of ink in paper fibers. After the expansion and absorption of ink in the paper fiber, the edge of the recording point will become blurred, which limits the edge definition of the recording point, and the adjacent recording points are likely to be crowded together, resulting in the de facto reduction of the resolution of the recording point. Too much ink penetrates into the paper, resulting in too thin ink layer formed on the final paper surface, which affects the optical density and tone performance of printing results. In addition, the expansion and penetration of ink will also prolong the drying time. In order to speed up the drying process, some equipment adopt the evaporation drying technology of forced hot air flow to treat the paper surface
there are three solutions to the problem of matching ink-jet printing ink with paper:
one is to make an article on ink. For example, HP Scitex series equipment, Agfa’s Jeti series equipment and Konica Minolta KM-1 all use UV ink, and use UV ink to dry quickly to solve this problem. Another example is Xerox triver 2400 uses high fusion phase change ink, and wax ink melts and ejects ink droplets, When the ink drops arrive at the paper surface, they will be colloidal after cold curing, so as to effectively prevent the penetration of ink on the paper surface
another solution is to pretreat the paper before printing and use water-based ink for printing, such as the inkjet printing equipment of Kodak, HP, Fujifilm and other manufacturers
the third scheme is to adopt the transfer method (that is, the ink drops are sprayed on the transfer blanket first, and then transferred to the paper surface after the ink evaporates to form an ink film). The equipment adopting this scheme include Landa S10 and Canon Voyager
there are many kinds of printing materials for packaging and printing. In addition to paper, plastic, metal, glass and various composite materials are also common. These materials generally have the characteristics of non absorbability to ink. UV ink can be used to solve the problem of ink drying in inkjet printing, but followed by the problem of the fixation degree of the dried ink on the surface of the printing material. At present, the main means to solve this problem is to pretreat the prepress surface of the printing materials. In addition, when UV inkjet printing is carried out on curved surfaces such as cans and bottles or surfaces often using deformed leather, there are high requirements for the flexibility of the ink layer after drying, which is a challenge for UV inkjet printing.

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