Photogravure ink printing problems and solutions

1, "Pear skin" pattern

Failure phenomenon: In the case of overprinting, when the second color ink covers the first color ink film, the formed ink film of the first color is dissolved, and the upper and lower two layers are partially blended, so that the film is in a scratched state.

Cause: The resin in the ink (like polyamide resin and rosin resin) is very soluble. It is prone to breakdown of the peel. The viscosity of the ink, especially the viscosity of the second color is too small, and the corresponding solvent is too much; the dryness of the ink, especially the dryness of the first color, is too slow, and the time for the solvent to run the first color ink is also long. Therefore, the chance and degree of destruction of the first color ink film is greater or greater.

Solution: Increase the viscosity of the second color ink, improve the dryness, and increase the amount of hot air to promote its quick drying.

2, ash (powdered)

Symptoms: The pattern of the print can be lightly rubbed off, or the pattern and text can be damaged in the process of moving and binding, the stain of the printed material contaminating the machine or the hands of the person contaminated.

Cause: This malfunction is similar to the phenomenon of “powdering” in plastics and lead marks. Due to the thick gravure prints, the amount of toner is large when the powder falls out, so it is called ash (powder). The main reason is that the ink is too thin, that is, the solvent is too much, and the resin that wraps the color is dissolved, or the resin in the binder is too little. When paper is printed, the paper absorbs a large amount of adhesive. After a large amount of solvent volatilizes, the paint is bare so that it cannot be adhered to the surface of the paper, but merely floats on it. Also, the molecular weight of the resin is too small, and the pigment and resin have poor wettability.

The solution: the ink itself is too thin, it had to re-ink. If it is improperly adjusted, it is necessary to add the same thick ink or add a thick, sticky varnish when mixing. If it is a paper problem, you must change the quality of the paper. If it is printed on a plastic film, this problem occurs and it is best to compound the process.

3, ink spots

Symptoms: Irregular, uneven filaments, dots, and looming patches appear on the dark side of printed matter. Gives people a sense of peaks or granular unevenness.

Cause: Because the viscosity of the ink is too low, the printing speed is too slow and the drying is slow. The ink sags in one direction like water. It may also be distributed in a high profile, and spotting occurs in shadows. Due to the poor fluidity of the ink, it is also relatively thick, the thixotropy is too high, the leveling property is not good, the amount of ink is insufficient, and spots easily occur. The solvent used is not compatible with the ink; either the wrong ink was misused and mixed with different types of ink; the use of a white, hydrated ink that was reused; or the gel was used but not sufficient Recovered inks; inks have poor wettability on printed matter. There is also the phenomenon of static electricity due to the depth of the plate; the pressure is unfavorable and the angle of the blade is not appropriate, causing the ink to spread and spread out irregularly.

Solution: Use a thicker ink or use too dilute ink with new ink; use the corresponding solvent to make the drying faster, and to make the solvent of the dissolved resin volatilize slightly slower than the co-solvent. Increase the fluidity of the varnish composition, the use of high viscosity and low thixotropic ink, it is a good leveling. Change the paper to match the ink, or reprocess the plastic surface so that the ink fully wets its surface. Use shallower plates; presses are slightly larger; squeegee pressure is reduced and angles become larger. Causes reasonable printing conditions.

4, hydration

Symptoms: The solvent composition in the ink changes, resulting in thickening of the thin ink, resin precipitation, gelation, reduced concentration, poor transfer, paste version and other problems, especially the pattern is small, less ink.

Reason: Due to the long-time printing, the moisture in the air, the polar solvents in the ink, such as alcohols, polar resins, resins containing amide groups, they have affinity with water and into the ink. Also because the solvent evaporates too quickly, it cools the surrounding air. The ink is in contact with the air for a long period of time, or water in the scene may accidentally enter the ink.

Solution: Replace old ink with new ink. Formulated with moderate volatile dissolution, delay dryness. The ink cover is well sealed. Check that the hair does not face the roller.

5, bite color

Failure phenomenon: In the color printing of satellite rotary gravure printing machine or unit combined rotary gravure printing machine, especially when printing polyolefin film, the second color ink will stick out the ink of the previous color printing.

Causes: Due to the slow dryness of the ink of the previous color, or its poor adhesion to the printed body, and the later color (ie, the second color), the adhesiveness is too large, the printing pressure is too high, and the amount of resin in the ink is too small. , can bite the previous color bite off; or printing speed is too fast, the former color has not yet dried, can not stand the second color splitting force; the same time, when printing, the hair is not focused on the pattern or the air volume is small, when adjusting In the first color, the solvent of the slow-drying component is too much, so that the former color cannot be adhered as required, and is dried and is damaged by the second color of the tack.

Solution: For the former color, you should speed up the drying, adding low-boiling solvents; slow down the speed; increase the amount of resin, add the ink with the resin, do not use pure solvents. The blocked part of the air duct is unblocked, and a tube with a narrow slit is formed on the surface of the impression roller, which may be too long and the wind rushes to the side. Measures should be taken to stick the overprinted part to make the wind blow over the printed pattern surface. on. When adjusting the viscosity, if there are too many slow-drying components, the original ink should be used for remedy. For the second color, the distance between the plate roller and the embossing roller should be adjusted to reduce the pressure; the viscosity of the second color should be slightly smaller than the previous color. Synchronize slows down. If the previous color is not strong enough to adhere to the printed material, check whether the film is treated at more than 38 dynes/cm. Otherwise, it should be re-treated or a resin-containing solution, such as gold slick, should be added to the ink.

6, post-press color is not required

Symptoms: Printing color is too strong or light color

Cause: The gap between the ink and the eye was not detected beforehand; the blindness was too great when the color was assigned. The ink is too thick and sticky and the dots are too deep. Or the ink is too thin, too light, and the dots are too light.

Solution: According to the design requirements, the method of wiping and contrasting on the same printed material at the scene is used to find the color that meets the requirements, and the principle of functional color of the ink subtractive color scheme can also be followed to deploy the desired color tone. According to the hue of the hue, increase or decrease the required ingredients, and do not greatly reduce the intensity. When the color is not clear, white ink of one to two percent can be adjusted to increase the brightness. For too thick, too viscous ink, solvent dilution can be added. For too thin, too light ink can be formulated with a relatively thick new ink. For the printing plate is too deep, too shallow can only be re-edition.

Source: China Ink Technology Network