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From the experience of printing materials

second, the influence on the ink color of printing

plate printing is a widely used production process. How to improve the quality and production efficiency of color printing is worth analyzing and discussing

the visual effect of printing ink is one of the important factors to measure the quality of printing. There are several situations that have a direct impact on printing ink before it can enter the market

(-) the influence of the thickness and viscosity of the printing ink layer on the ink color of the print

an appropriate printing ink layer is an important measure to ensure the ink quality of the print and prevent the print from sticking. If the ink layer is too thick, its viscosity is bound to increase, which is easy to produce paper fuzzing, affecting the uniformity of the ink color of the print first. If the ink layer is too thin and the ink viscosity is insufficient, the ink color printed will be weak, and the visual effect of the print will be poor. With the extension of the printing machine rotation time or the acceleration of the printing speed, the friction coefficient increases, and the ink temperature will gradually increase. Therefore, the ink will become thinner and its viscosity will decrease accordingly. Therefore, these conditions must be comprehensively considered when adjusting ink to ensure that a relatively balanced printing ink color is obtained for batch products. However, in the actual production process, the decline of ink viscosity is inevitable. Often the ink color of the printed matter is thicker at the beginning of printing, and then it will become lighter. You can increase the ink supply by appropriately adjusting the rotation angle of the ink transfer iron roller to keep the consistency of the ink color before and after. In addition, in order to prevent the ink viscosity from changing too much and affecting the balance of the ink color of the print, the contact between each rubber roller and the ink string iron roller should not be too tight, and the colloid should not be too hard, so as to minimize the friction heat and maintain the appropriate concentration of the ink

(II) the influence of printing pressure on the ink color of printed matter

printing pressure is one of the important conditions to realize the transfer of imprints. Because the surface of the printing plate is not absolutely flat, there are inevitably subtle concave convex and uneven thickness on the surface of the paper. If the printing pressure is insufficient or uneven, the printing ink color on the plate will inevitably appear uneven. Therefore, the ideal printing process is based on the "three levels" (that is, the printing plate is relatively flat with the inking roller and the lining body to obtain good contact conditions), with a thinner ink layer through the role of balanced printing pressure, so that a more uniform ink color can be obtained on the print. If the printing pressure is insufficient or uneven, there is a poor contact between the lining body and the printing plate surface, the visual effect of the ink color of the printing plate can be satisfied by increasing the ink delivery volume, but this will not only increase the consumption of ink, but also prone to printing sticking, which is not desirable

(III) influence of cot quality on prints and ink color

as for embossing and flat printing process, whether prints can obtain ideal ink color is closely related to the quality of cots. There are five or six, or even more than 10, ink transfer rollers, leveling rollers and inking rollers in the equipment for printing color printing, among which the ink transfer rollers and inking rollers have a greater impact on the ink intensity. The quality of COTS is mainly reflected in elasticity, viscosity, center of circle and surface finish, while the viscosity mainly affects the intensity of ink. In the printing process, only when the cots maintain a certain viscosity, can we ensure that the amount of ink coated on the plate is uniform in each printing cycle. However, in the actual production process, the viscosity of the rubber roller is not stable. First, due to the increase of paper dust in the ink, it is covered with a dust cover when not in use to prevent the invasion of dust, which affects the viscosity of the colloid; Secondly, the tackifier (glycerin) on the colloidal surface is lost with the increase of temperature and the extension of service time. The viscosity of the surface of the rubber roller gradually decreases, and the ink absorption performance correspondingly decreases. The electronic universal data experiment motor universal data experiment machine is a mechanical universal experiment machine controlled and tested by electronic technology, which affects the balance of the ink color of the printing. Therefore, polyurethane Cots with stable quality should be used for printing plate products. If printing bulk products, the cots should be cleaned in time

(IV) the influence of different paper cleanliness on the ink color of printed products

in fact, the relationship between paper and ink is complex. If you only consider the ink color of a book, you should note that the smoothness of the paper surface has a certain relationship with the ink color. If the pressure of each version is the same, the smoothness of the paper surface is inversely proportional to the ink consumption, and the ink absorption of smooth fans is small, on the contrary, the ink absorption is large. Therefore, if there is a difference in the smoothness of the front and back surfaces of the paper, the method of increasing the ink volume and pressure should be adopted as appropriate, and appropriate adjustments should be made. In printing, it is customary to print smooth surface first, and then rough surface. When printing, appropriately increase the pressure and ink supply, so that the ink color on both sides presents an ideal visual effect. Practice shows that the effect of using the above method is much better than simply increasing the ink output, and the printing quality is better

(V) the influence of light changes on print ink

generally, there are three light sources to identify print ink: sunlight, fluorescent lamp and electric lamp. The color of the light emitted by these three light sources will be different due to their different luminescence conditions. The eyes are pure white light, the fluorescent lamp is white with blue, while the electric light is red and slightly yellow. Although the light sources of sunlight and fluorescent lamps are somewhat similar, the differences between them should be taken into account when identifying products with high quality. The influence of light on the identification of ink color lies not only in the light source, but also in the intensity of light and the irradiation angle. Under the same light source, the intensity of the reflected light on the illuminated sheet is mainly determined by the distance between the sample sheet and the light source, and the near is strong and the far is weak. The correct irradiation angle should be that the incident angle is equal to the reflection angle. Light irradiation on the sample inevitably has partial refraction, but it has little effect on the identification of ink color. When identifying the ink color of printed matter, whether in the daytime or at night, it should be carried out under the condition that the intensity of the light source and the irradiation angle are the same, so as to prevent color deviation or ink color variation caused by ink mixing errors

(VI) influence of overprint inaccuracy on ink color

whether the overprint of various color printing plates is accurate will have a great impact on the printing hue. Overprint accurate hue effect is also good, overprint inaccurate print hue will be biased. This is due to the position difference of overprint of various color points, which will inevitably produce visual color difference. Therefore, overprinting of the printed color products must be accurate to ensure that the printing hue meets the process requirements. In order to prevent the color deviation caused by inaccurate overprinting caused by the expansion and variation of the paper, for the point color products with high quality requirements, it is advisable to use the multi-color machine to complete the color stacking printing at one time, so as to improve the overprinting quality. In addition, the paper should also be hung and dried to reduce the occurrence of sheet variation in the printing process

(to be continued)

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