11 major problems and solutions of ink in gravure printing process - Company news - Zhangjiagang Free Trade Zone kworld Chemical Technology Co., Ltd.

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11 major problems and solutions of ink in gravure printing process

2022-07-26 13:35:00

Gravure ink is prone to some problems during the printing process. How to solve these problems? In this article, Plastic Box will give you a brief introduction to 11 major problems and solutions that are prone to occur in gravure ink printing.
Causes and solutions:

(1) The surface tension of PE or PP film is lower than (3.6-3.8×10-2N/m). The surface tension measuring solution is used to check the surface tension of the film. If it fails to meet the requirements, it should be reprocessed.

(2) The ink is diluted too thin, the binder is damaged or the thinner is used incorrectly. When diluting the ink, it is advisable to control the viscosity within 25-35 seconds (coating 4# cups). In addition, the choice of thinner should be careful, do not misuse it, so as not to affect the quality of the ink.

(3) The adhesion fastness of the ink itself to the film is poor. The ink variety should be replaced or the ink manufacturer should be contacted.

1. The imprint is lost

Phenomenon: During the printing process, the small characters and thin lines are lost at the beginning, and the pattern cannot be printed in severe cases.

Causes and solutions:

(1) The viscosity of the ink is too high, which does not match the printing speed. Adjust the ink viscosity to an appropriate value.

(2) The ink drying speed is too fast, and the printing speed is too slow. Add slow-drying diluent (or n-butanol slow-drying solvent) to the ink, but the amount added should be strictly controlled.

(3) The mesh hole of the printing plate is too shallow and needs to be remade.

(4) The angle and position of the scraper are improper. The normal squeegee angle is generally between 30-60°, which can not only keep the blade from hurting the plate, but also the printing ink layer is better. The position of the scraper depends on the drying conditions of the ink. If the ink dries too fast, the scraper can be moved forward appropriately to shorten the distance between the scraper and the imprinting point.
(5) The position of the hot air is improper, and the position of the hot air is adjusted.

3. Ink overflow

Phenomenon: There are spots, patterns on the solid printing surface, or the ink overflows from the line part.

Causes and solutions:

(1) The viscosity of the ink is low after dilution. Add part of the original ink and adjust the viscosity for 25-35 seconds (the current task is 4# cups); or print on an empty machine for a period of time, so that part of the solvent evaporates, and the viscosity of the ink is increased to a suitable value.

(2) The printing speed is too slow, or the ink drying speed is too slow, increase the printing speed, or adjust the drying diluent to the ink.

(3) The mesh of the printing plate is too deeply engraved or severely worn, and the plate needs to be remade.

(4) The hardness, pressure and angle of the scraper are not appropriate. Adjust the pressure and angle of the scraper, grind the blade edge of the scraper, and reduce the hardness.

4. Eat color

Phenomenon: During overprinting, the ink on the printing plate of the latter color sticks the imprint of the ink of the former color on the substrate, and is reversely printed on the printing plate of the latter color.

Causes and solutions:

(1) The thorough drying of the previous color ink is not good. The former color ink is added with fast drying diluent to improve its drying speed and make the latter color ink slower than the former color ink.

(2) The adhesion fastness of the previous color ink is not good, replace the ink.

(3) The printing speed is too fast, the engraving of the printing plate is too deep, the printing pressure is too large, reduce the printing speed, strengthen the drying function, reduce the pressure of the printing roller or use a shallow version.

(4) Improper use of diluent, check and replace with appropriate diluent.

5. Adhesion

The adhesion phenomenon can be roughly divided into three situations.

(1) The adhesion that occurs after the printed matter is rolled up to the time of bag making is called "primary adhesion".

(2) The adhesion phenomenon that occurs in the bundle of plastic bags when the stored bags are packed is called "secondary adhesion".

(3) The adhesion that occurs after packaging is called "tertiary adhesion".

Causes and solutions:

Generally speaking, the main factors that cause adhesion are pressure, temperature, relative humidity and time.

Primary blocking is mainly due to residual solvent or winding tension in the blot. This is because the volatilization speed of the diluent in the ink is too slow or the printing speed is too fast, and the drying effect of the drying system is poor, the engraving of the printing plate is too deep, and the ambient temperature and humidity are too high. As long as the appropriate ink thinner is selected, the printing speed is reduced, the drying effect of the drying system is enhanced, the ambient temperature and humidity are improved, the winding tension is appropriately reduced, and the plate cylinder with shallower cells is remade. One sticking problem.
Secondary adhesion is mainly affected by the temperature and humidity in the storage environment of the product, mainly because the ambient temperature or relative humidity is too high, which makes the ink soften, sticky or redissolve, thereby causing adhesion. For example, the ink can withstand 50 ℃ temperature under normal circumstances, but when the relative humidity increases by 10%, its heat resistance will drop to only 45 ℃. For this reason, as long as the ambient temperature and humidity are well controlled, secondary adhesion can generally be prevented.

The third adhesion is mainly caused by the contents inside. Due to the permeability of PE and PP films, when used to package items containing alcohols, esters, flavors, etc., such as balsam, liquid cosmetics, ginger, mustard greens, curry powder, etc., the exudation of alcohols, esters, flavors, etc. And migrate to the ink layer to redissolve the ink layer and cause adhesion.

6. Albino

Phenomenon: There is a layer of white frost on the surface of the blot.

cause:

(1) Solvent whitening: The main reason is that solvents with large latent heat of volatilization are used in the ink, such as alcohol solvents. When the relative humidity of the environment is too high, the excavation of the solvent in the imprint causes the temperature of the imprinted ink layer to drop, and the air collects. The water falls onto the surface of the blot, forming a layer of white frost.

(2) Resin whitening: Due to the different volatilization speed of the solvent in the ink, the solvent is out of balance. The main reason is that the volatilization speed of the real solvent is faster than that of the diluent, so the proportion of the diluent in the ink increases. To a certain extent, it will cause the resin to precipitate out, thus forming a layer of hoarfrost-like substance.

Solution:

(1) To reduce the relative humidity of the environment, it is best to maintain constant temperature and constant humidity printing conditions.

(2) Strengthen the drying effect of the drying system.

(3) Use slow drying solvent instead.

(4) Add some solvent with slow volatilization speed, or adjust the solvent ratio.

7. Water pattern or splash

Phenomenon: The solid part of the printed matter is not full, and there are wavy patterns.

Causes and solutions:

(1) The ink viscosity is low. Supplement appropriate original ink, or add high-viscosity continuous material.

(2) The printing speed is slow. Appropriately increase the printing speed.

8. Circular markings

Phenomenon: The imprint is uneven, and there are irregular spots on the solid part.

Causes and solutions:

(1) The thixotropy of the ink is large, the leveling is poor, or the ink is too diluted and the viscosity is low, the ink should be replaced or the viscosity of the ink should be increased.

(2) The drying speed is too fast and the printing speed is too slow. Add slow drying thinner and adjust printing speed.

(3) The mesh of the printing plate is not appropriate (generally deep), and it needs to be re-engraved for plate making.

(4) The influence of static electricity. Add a device to eliminate static electricity, or add an antistatic agent to the ink.

9. Bubbles

Phenomenon: tiny bubbles are produced in the ink, and small blank dots appear in the imprint.

Causes and solutions:

(1) A large amount of air is mixed in the ink tank. Use a defoamer to reduce the amount of air bubbles.

(2) The drop of the ink when it returns to the ink tank is too large. Adjust the ink tank position and height.

(3) The ink storage time is too long. Add some new ink or replace all.

(4) The printing speed is too fast. Appropriately reduce the printing speed.

10. Blocked version

Phenomenon: The ink dries and solidifies in the cells of the printing plate, resulting in the lack of drawing or disconnection of the text and lines of the printed matter, and the pattern cannot be printed in severe cases.

Causes and solutions:

(1) The distance between the contact point of the scraper and the imprinting point is too large. Reduce the distance between the blade contact point and the imprint point.

(2) The printing speed is slow. Increase printing speed.

(3) The ink drying speed is too fast, and it has been dried in the printing plate cells before being transferred to the substrate. Add a slow drying agent to the ink to reduce the drying speed of the ink.

(4) The ink particles are too large or mixed with other impurities. Filter the ink or replace the ink.

(5) The printing plate is not cleaned, and the residual ink is dry and solid in the mesh, causing blockage. Thoroughly clean the plate.

11. The ink is jelly

There are two cases, one is that the ink that has just been pulled from the warehouse is in a jelly-like state and cannot be poured out of the ink bucket. This phenomenon generally occurs in winter and spring, which is caused by the poor low temperature resistance of the continuous material in the ink. If the jelly-like ink is light, shake the ink tank gently to destroy this property, and then it can be used on the machine. If the jelly of the ink is heavy, it should be stored at room temperature for a day and night, and then used after the ink returns to normal.

Another situation is that during use, the fluidity of the ink gradually deteriorates until it becomes jelly and cannot flow, which is mainly caused by improper use of diluents (such as only alcohol or stupidity), or it may be The alcohol content is too high. When the relative humidity of the environment is too high, due to the hygroscopic effect of alcohol in the ink, the moisture in the ink increases over time, resulting in poor ink fluidity or even jelly. This situation is rare, the ink can be replaced again, and a little frozen ink can be added to the new ink. In order to prevent this from happening, less diluent should be added each time the ink is adjusted, and some new ink should be added at the same time to ensure the stability of the ink composition.

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