The characteristics of three major printing materials and the use of skills

The competition in the packaging market is now fierce, and competition in this area will intensify in the future. In the future, only those businesses that can provide good print quality may win the buyer’s favor. The use of flexographic printing techniques on porous substrates, such as corrugated board (including pre-printing and post-printing), folding cartons, paper bags, etc., requires in-depth knowledge of the characteristics and use of inks, plates, and anilox rolls. In order to effectively improve the quality of the entire printing process.

Ink

In the event of a print quality problem or when the printing standard cannot be met, ink is the scapegoat to bear the brunt. In order to obtain a good print quality, you need to understand the characteristics and application skills of the ink itself:

â–  Viscosity: In the days prior to planning a print job (especially before major and complex print jobs are performed), the ink modulator needs to be responsible for the print job (printing process, ink block, overprint combination, etc.) The composition of the anilox roller and the printing speed to be set are fully understood. Only in this way can the ink viscosity be adjusted according to the printing needs.

â–  pH: In addition to the ink viscosity and all of the above information, the ink modulator also needs to determine the correct ink pH for the best printing results. It is worth noting that the pH of water-based inks will gradually decrease, especially during printing or long-term exposure to air (without the lid of the ink cartridge). Therefore, when the ink is not used, close the lid of the ink cartridge. As the pH decreases, the ink viscosity increases. Only when the pH is adjusted back to the standard state (8.2 to 9.0), the viscosity of the ink can be restored to its normal state. Changes in viscosity during the printing process will not only lead to changes in printing color, but may also lead to the emergence of other problems such as dirty printing, outer edge banding, reduced color wear resistance, and the like. Therefore, it is very useful to install a printing linkage unit for automatic ink viscosity or pH adjustment devices designed for high-end users.

â– Color: Everyone wants the color of printed products to meet the regulations. In addition, there are some considerations:

- The same amount of substrate/paper must be used for actual printing and proofing

- The same printing equipment must be used for actual printing and proof printing with the same printing speed, parameter settings, printing plates, anilox rolls and other parts.

- Printed colors and standard printing colors must be compared under the same lighting conditions.

According to international laboratories and quality control (QC) reporting requirements, color assessment also includes the comparison of the color viscosities of the two printing results. That is, if the viscosity of the two printing results is not the same, even if it falls within the allowable error range of the colorimeter, It is not possible to obtain the QCPASSED label.

In order to keep the ink in good condition after use, in order to ensure that the ink is still stable after a few days of use, there are some minor details to be aware of:

â–  Never add water to the ink to dilute the color density of the ink, especially when working under high-temperature long orders. Please use the designated diluent recommended by the ink supplier.

â–  Advise the operator not to bring excess moisture (excluding moisture from the cleaning drum) into the ink cartridge each time the printing is completed.

â–  Before reloading the ink into the ink cylinder, it is necessary to re-determine and adjust the ink specifications through the International Quality Control (QC) and Quality Assurance (QA) systems. This includes re-adjusting the ink viscosity, pH, and color back to the original standard.

Printing plate

Before using the plate, there are several parametric criteria that require special attention:

■ Hardness: The appropriate plate must be carefully selected for the needs of different types of printing jobs. Fine print designs include dots, small letters, bar code printing, and require higher hardness plates, eg, 55° Shore A; cardboard printing requires slightly lower hardness of the plate, which is approximately between 36° and 38° shore A.

■ Adhesiveness: Plates with too high adhesiveness are likely to cause “dirty” printed products because dust or other dirt on substrates tends to adhere to the plate, and in the long run it will cause the plate to carry ink. The capacity of the city is weak, and the color density of printing drops.

â–  Surface Tension: Examining the surface tension is particularly important for photosensitive resin plates because some of the processes involved in making such plates, such as cleaning and disassembling, may cause changes in the surface tension on the finished plate.

â–  Cleaning: Thorough cleaning is required for both rubber and photosensitive resin plates. Dry ink agglomerates and cardboard dust adhered to the plate should be removed after each use. If it is not clean, the printing quality will be reduced, the ink transfer ability will be weakened, and the service life of the printing equipment will be shortened.

Finally, the plates should be subjected to regular hardness tests, especially after printing 200,000 sheets. Once the stiffness of the printing plate has significantly increased or decreased, a new printing plate needs to be replaced.
(to be continued)