Core Information: If the ink on the embossing printing cylinder is not scraped clean, the ink in the printing ink tank will become thickened. As a result, the printed products may exhibit problems such as lack of color, dirtiness, ink bleeding, knife streaks, and knife lines. The dirtiness and ink bleeding of the printed products are related to the adjustment of ink viscosity.
 
1. Evaluate the adaptability and transferability of the ink scraper.
If the ink cannot be scraped clean on the cylinder of the intaglio printing plate, and the ink in the ink tray becomes thickened, the printed products will exhibit phenomena such as lack of color, dirtiness, ink bleeding, knife streaks, and knife lines. The dirtiness and ink bleeding of the printed products are related to the adjustment of ink viscosity. The temporary layering of the ink can cause dirtiness, and high ink viscosity will result in ink streaking. However, it is closely related to whether the angle and pressure of the scraper device are correct and appropriate. Only when the ink cannot be scraped clean on the full printing plate cylinder and cannot be scraped clean even after pressing with fingers or replacing with new ink, it may indicate that the ink is faulty. If the ink can be scraped clean after replacing with new ink, then it is a problem with the added diluent in the ink.
The solution is: replace the ink or diluent and re-adjust the scraper.
2. Inspection of the printing substrate (plastic film).
If the ink shows phenomena such as missed printing, white spots, orange peel color, and poor adhesion, the first step is to test the surface tension and static electricity of the printing substrate. If the surface tension of the printing substrate is lower than 35 dyn, the adhesion of the ink will be poor. High static electricity will cause orange peel color, ink spots, ink tendrils, and the ink drying too quickly will cause blockage of the plate, resulting in missed printing and white spots on the printed products.
The solution is: re-treat the printing substrate, install static elimination equipment in the relevant parts of the printing machine, increase the humidity in the working area, and adjust the drying speed of the ink with a slow-drying solvent. If the ink is diluted, the printing speed can be increased and the effect will be better.
3. Inspection of the purity and odor of the diluent.
If the purity of the diluent in the original ink is poor, the solvent residue in the printed products will increase, and the odor may remain on the printed products.
First, check the purity of the solvent. A simple test method is: place an 8 (m wide) white paper strip in the solvent to soak, then take it out and slightly press it with force, observing the speed of solvent drying on the white paper strip or whether it changes. After waving the white paper strip for 8 to 15 times, if the solvent dries normally, it is normal; if not, the drying speed is slow; otherwise, the drying speed is fast. If the white paper strip changes color, except for the color of the solvent bucket and rust, it indicates that the solvent is problematic. If there is a residual odor after the solvent evaporates, it means the purity of the solvent is insufficient. If there is a residual odor when smelling the scraped sample of the original ink, the ink is problematic. If there is an odor in the scraped sample of the diluted ink, it indicates that the solvent used for the diluent is not pure.
The solution is: replace the ink or adjust the solvent of the diluent.
4. Correct use of retardants.
The retardants in the ink, or incorrect use of the retardant diluent during printing, can cause the printing to have the phenomenon of color eating (or dissolving), and the printing products to appear false drying or reverse adhesion.
The solution is: change the diluent formula of 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 the ink during printing can adjust the drying performance of the ink, can adjust the color concentration of the ink, and can also adjust the viscosity of the ink. Adjusting the drying property of the ink is conducive to improving the printing speed and the clarity of the printing products. Adjusting the color concentration of the ink can reduce the pressure on the impression roller or the workload of the ink knife, which is beneficial to the increase of the printing speed. Adjusting the viscosity of the printing ink is precisely the key to controlling the ink application amount or adapting to the printing speed and the room temperature of the printing place.
The solution is: according to the printing speed, the depth of the graphics on the printing plate roller (roll), the room temperature of the printing place, mix fast-drying, medium-drying, slow-drying or extremely slow-drying diluents.
6. Usage from high viscosity to low viscosity.
For high viscosity, the graphics on the printing plate are relatively deep. It is necessary to use ink with high viscosity for printing; otherwise, the patterns on the printing products will form water waves due to the low viscosity of the ink. When the printing speed is fast, the graphics on the printing plate are relatively shallow, and low-viscosity ink should be used for printing; otherwise, due to the high viscosity of the ink, the ink application amount will be insufficient or the ink will be missed, and the printing machine will also have an increased workload due to the high viscosity of the ink, causing the printing speed not to be able to increase.
The solution is: use diluents and diluents to adjust the viscosity of the printing ink.
7. Use of spot color ink and metallic ink, and the use of ink rollers.
For spot color printing, the ink color and uniformity must be consistent. In metallic ink, copper and gold powder are prone to settle, so it is very necessary to use a uniform ink roller in the printing process. The ink pan should also be placed with a stirring rod. In addition, in the use of spot color ink, diluents should be used in combination with diluents, and it is not advisable to use solvents alone to dilute. Metal ink should not be diluted with solvents. The correct method is to add a certain amount of diluents to adjust.
8. Use of non-solvent and mixed use.
Although non-solvent solvents cannot dissolve the coupling resin in the ink, by using this characteristic, they can be mixed with true solvents to dilute the ink and reduce the viscosity of the printing ink, which can alleviate the phenomenon of color eating (or dissolving) during printing.
9. Inspection of the adhesion of the printed products,
Use a tape to stick on the printed product, press it flat with your fingers, and make it closely adhere to the printed product. Then slowly peel off the entire length by half, and quickly peel off the other half. The less ink that is left on the printed product, the stronger the adhesion of the ink to the printed product is, and vice versa, the adhesion is poor. If more than 40% of the ink on the printed product is peeled off, it indicates that the adhesion of the printing ink on this printed product is unqualified.
 
Source:(ahprint.com)