1. Determine the adaptability and transferability of the ink scraper.
If the ink on the gravure printing cylinder cannot be scraped clean, and the ink in the printing ink tray becomes thick, the printed products will exhibit issues such as not coloring, smudging, ink running, blade threads, and blade lines. The smudging and ink running of printed products are related to the adjustment of ink viscosity. A temporary stratification of the ink can cause smudging, and high ink viscosity can lead to ink running, but it is closely related to whether the angle and pressure of the scraper device are correct and appropriate. If the ink cannot be scraped clean from the fully inked printing cylinder, even when pressing with a finger or replacing with new ink, it may indicate a problem with the ink. If the new ink can be scraped clean, then the issue lies with the diluent added to the ink.
The solution is: replace the ink or diluent, and readjust the scraper.
2. Inspection of the printing substrate (plastic film).
If the ink shows signs of missing prints, white spots, orange peel texture, or poor adhesion, the first step is to check the surface tension and static electricity of the printing substrate. If the surface tension of the printing substrate is below 35 dynes, the adhesion of the ink will be poor. High static electricity can cause orange peel texture, ink spots, and ink hairs, and if the ink dries too quickly, it can lead to plate blocking, resulting in missing coatings and white spots on the printed products.
The solution is: perform surface treatment on the printing substrate, install static elimination devices in relevant parts of the printing machine, increase humidity in the working environment, and adjust the drying speed of the ink with slow-drying solvents. If the printing ink is diluted, it can improve the printing speed.
3. Purity and odor inspection of the diluent.
If the purity of the diluent in the original ink is poor, the solvent residue on the printed products will increase, and there may also be residual odors on the printed products.
First, check the purity of the solvent. A simple testing method is: tear an 8 cm wide strip of white paper and dip it into the solvent to moisten it, then take it out and swing it with some force, observing the drying speed of the solvent on the white paper strip or whether it changes color, and then smell the white paper strip for any residual odor. If the solvent evaporates and dries after swinging the white paper strip 8 to 15 times, it is normal; if it does not dry, the solvent has a slow evaporation rate, and vice versa. If the white paper strip changes color, except for rust from the solvent barrel, it indicates a problem with the solvent. If there is a residual odor after the solvent evaporates, it indicates insufficient purity of the solvent. Test the scraping samples of the original ink and diluted ink on a film after drying. If the scraping sample of the original ink has a large residue and the scraping sample of the diluted ink has a small residue, it indicates normality; otherwise, the diluted solvent has a problem. If the scraping sample of the original ink has a residual strange odor, then the ink has a problem. If the scraping sample of the diluted ink has an unusual odor, it proves that the solvent used in the diluent is impure.
The solution is: replace the ink or adjust the solvent of the diluent.
4. Correct use of slow-drying agents.
If the slow-drying agent in the ink or the slow-drying diluent used during printing is incorrect, it can lead to color biting (eating or dissolving) during printing, resulting in false drying or re-stickiness in the printed products.
The solution is: change the formulation of the diluent for the printing ink, adjust the drying performance of the printing ink, and increase the printing speed.
5. Application of different ratios of diluents.
Different ratios of diluents in printing can adjust the drying performance of the ink, adjust the color concentration of the ink, and adjust the viscosity of the ink. Adjusting the drying properties of the ink is beneficial for increasing printing speed and improving the clarity of printed products. Adjusting the color concentration of the ink can reduce the pressure on the impression rubber roller or the workload of the ink scraper, which is conducive to increasing printing speed. Adjusting the viscosity of the printing ink is key to controlling the amount of ink applied or adapting to the printing speed and the room temperature of the printing environment.
The solution is: prepare fast-drying, medium-drying, slow-drying, or very slow-drying diluents according to the printing speed, the depth or line count of the graphic design on the printing cylinder, and the room temperature of the printing environment.
6. Usage method from high viscosity to low viscosity.
For slow printing speeds and deeper graphic designs on the printing plate, high-viscosity printing ink is required; otherwise, the patterns on the printed products may form ripples due to the low viscosity of the ink. For fast printing speeds and shallower graphic designs on the printing plate, low-viscosity ink should be used; otherwise, the printed patterns may suffer from insufficient ink application or missing coatings due to high ink viscosity, and the printing machine may also experience increased workload on the scraper due to high ink viscosity, resulting in reduced printing speed.
The solution is: use diluents and thinners to adjust the viscosity of the printing ink.
7. Use of ink rollers for special colors and metallic inks.
Special color inks require consistent and uniform ink color, and metallic inks with copper powder are prone to settling, so it is very necessary to use ink rollers during printing. Additionally, a stirring stick should be placed in the ink tray. Furthermore, when using special color inks, the diluent should be used in conjunction with the thinner and should not be diluted with solvent alone. Metallic inks should not be diluted with solvents; the correct method is to add an appropriate amount of thinner for adjustment.
8. Use and mixed use of non-true solvents.
Non-true solvents, although they cannot dissolve the binding resin in the ink, can utilize this characteristic to mix with true solvents to dilute the ink, which can reduce the viscosity of the printing ink and alleviate the color biting (eating or dissolving) phenomenon during printing.
9. Adhesion test of printed products.
Use adhesive tape to stick to the printed product, press it flat with your finger, and ensure it is tightly bonded to the printed product. Then slowly peel off half of it, and quickly peel off the other half. The less ink that comes off from the printed product, the stronger the adhesion of the ink on the printed product; conversely, if more than 40% of the ink is peeled off from the printed product, it indicates that the adhesion of the ink on this printed product is unqualified.