Most of the inks only focus on the determination of viscosity, but ignore the inspection of the adhesion, the printing ink adhesion fastness is not good or the paste version, the color concentration, the poorer the printing, can not improve the printing speed, after the color will be the same color The printing ink film is pulled off and the like, resulting in the falling off of the ink film of the printing image and the reduction in the authenticity rate after dyeing and cross-linking. The structure of various packaging printers and the performance of various types of substrates are different, so there are various requirements for inks. Therefore, the relationship between the viscosity and adhesiveness of various types of printing inks and the suitability of packaging and printing are interrelated. Again very complicated.
1, the relationship between the viscosity of printing ink and printing adaptability
Viscosity of ink, whether it is for letterpress or flexographic inks, high viscosity ink, slow printing speed, only suitable for letterpress and offset sheet or manual screen printing, low viscosity ink, fast printing speed, offset printing, flexible for high speed rotary printing And gravure.
For example: Rotary printing book inks are more viscous than printing newspaper inks. Another example is that the rotary gravure ink is smaller than the rotary offset newspaper ink. When the viscosity of the printing ink increases with the printing speed, the temperature of the ink increases after the ink roller rubs against the printing plate, and the ambient temperature rises, and the viscosity of the ink gradually decreases. A slightly higher viscosity will not affect the normal print job speed. Excessive viscosity not only affects the print fastness, but also affects the print job speed. In addition, different substrates require different ink viscosity requirements. Smooth, strong paper uses high-viscosity inks, while paper loose papers do not.
2. The relationship between printing ink adhesion and printing adaptability
Adhesion refers to the adhesion or adhesion between the ink and the substrate. In the past, people mistakenly thought that a printing ink with a large viscosity had a large adhesion force. Through practice, it has been found that the viscosity of some printing inks varies greatly. The fastness of its printing is very similar. As a technical indicator for packaging printing inks, inks should be selected for ink adhesion. Because the size of adhesion not only determines the quality of the gloss, adhesion, hiding power, color density, etc., but also determines the amount of printing.
Usually in the study of adhesion, we should pay attention to the relationship between ink color and adhesion, the adhesion of the latter color ink can not be greater than the previous color, otherwise it will pull down the previous color ink on the printing (often called dyeing, etc. malfunction). In order to prevent the above-described failures, the packaging and printing operator adds as many true solvents as possible to the ink system to be printed first when adding the ink thinner, and it is preferable to add more diluent to the ink system to be printed later.
2.1 Adhesion
Adhesion of Packaging Printing Ink If the printing conditions permit, the higher the viscosity of the ink is, the better the printing can be. The printed ink can be diluted or adjusted to increase the number of printed products.
Selecting adhesion should take into account the ink's printability. The ink stickiness meter was used to measure the adhesion of the ink at different rotation speeds so that each ink has a good overprinting property. For example, when the ink head is too long, because the formed filaments will be drawn back, it is possible that the printed product will have spots, and its printing dots will not be as complete as the relatively short inks. For engraved gravure or photosensitive flexible letterpress inks, the long silk ink is not easy to wipe on the plate and so on.
Determining the adhesion of an ink at a certain speed is very important because faster speed means greater separation force. It can be seen that the printing speed of the packaging printing press is closely related to the printing performance of the ink. An ink may be very smooth at a low speed and may fail at a high speed. For example, pulling paper (peeling), beard, pinhole, shrinking, spotting, flying ink, drawing less ink (poor overprint performance), picking dirty and so on.
2.2 Effect of Adhesion Additive on Packaging Printing
Over the years, in the printing process, the printing ink usually fades or becomes lighter due to various factors such as the increase or decrease of the pH value or the separately added ink or diluting agent, or thinner. There is no ink at the printing speed (often called roll off or no ink). Cross-linking and coupling agents can be added to increase the viscosity increase and gloss and adhesion. In addition to the gelation, re-coating of the ink, and the blockage of the ink roller or printing plate mesh (line), the viscosity increases. Big Shadow II is heading toward normal printing production. Although China has developed a viscous inspection principle and an ink stickiness value-added inspection method (see QB564-33), it often accuses ink producers or packaging and printing units of inferior products, and does not seriously study and analyze the causes and hazards of adhesion value-added. . Therefore, only by communicating or proposing a more reasonable printing production process, can we make up for the defects of packaging and printing products caused by ink. Only by grasping the viscosity and viscosity of the printing ink can we effectively improve the printing capacity and reduce the printing ink cost. Genuine printing rate. (Text / Liu Jiaju)