Plastic gravure ink printing failure analysis

Blocking, poor ink transfer, and missing dots are the most common and inconspicuous faults in gravure printing. Therefore, various factors should be taken into account in handling, and targeted measures should be taken to deal with them.

Block version

In gravure printing, the phenomenon of blockage is generally manifested as: shallow dot plate version can not be transferred (such as human skin color); deep dot plate ink transfer volume is reduced, usually from 50% to 70% down to 20% to 30%.

cause:

1 During printing, the viscosity of the ink caused by the solvent evaporation increases, and it is impossible to enter the fine cells or the network cable, causing the ink to gradually dry and cause blocking.
2 During printing, the distance between the squeegee and the plate cylinder is too large or the angle is unreasonable; due to the large diameter of the plate cylinder or the depth of entering the ink tank, the hot air blown from the drying equipment affects the plate cylinder, which also causes blockage. Version. This situation is very common in domestic printing presses.
3 The engraving depth of the printing plate and the angle of the cell site are not suitable.
4 printing environment temperature is too high, so that solvent evaporation speed is too fast, resulting in blocking plate.
5 With the addition of a series of curing agent inks, as the machine time increases, the ink cures in the plate cavity, gradually reducing the depth of the plate and causing blockage.
6 Insufficient design of ink formulation, using a solvent that dries too fast.
solution:
1 Adjust the ink drying speed, according to the actual situation, use slow-drying solvents.
2 Adding a varnish to improve and increase the fluidity of the ink.
3 After printing, immediately clean the plate.
4 According to the actual printing situation, add the appropriate solvent in time, try to ensure the consistency of the ink printing viscosity.
5 Redesign the ink formulation to reduce the initial dryness of the ink and the dryness of the ink and increase the fluidity and transferability of the ink.
6 For blockage caused by curing agent, hardener should be added as little or as little as possible; if it is really necessary to add curing agent, always check whether there is any blockage and handle it in time.

2. Poor ink transfer

In printing, due to poor transferability, the amount of ink transferred to the plastic film does not meet the requirements for the color density or color saturation of the original design and the standard printing sample, and printing failure occurs.
cause:
1 Blocking caused by printing, ink drying on the plate is too fast.
2 The selected ink does not match and cannot be adhered and adhered to the plastic film.
3 Incorrect ink formulation results in light ink color or insufficient ink saturation.
solution:
1 Because of the failure caused by printing blocked plates, it is necessary to analyze the reasons for blockage and take corresponding countermeasures.
2 Replaced with matching ink types.
3 improve the ink formulation, targeted selection of suitable raw materials, such as the use of strong color saturation and high coloring pigments and transfer of good resin.

3. Missing dot

During the printing process, the even flat screen on the printing plate can not be leveled because of the ink, and the dots appear alone, forming a filter-like network, and even missing dots. Generally starting from the second color group, this phenomenon is more obvious.
cause:
1 ink viscosity or yield value is too high, resulting in poor ink transfer.
2 The ink dries too fast, is not evenly distributed on the plate, and is prematurely dried and solidified.
3 Poor wettability between the ink and the plate (surface tension does not match), the transferred ink is not easy to spread.
4 The pressure of the blade is high, but the pressure of the printing roller is insufficient.
5 printing plate cable is too thick, the gap between the large network, the ink is not easy to spread.
solution:
1 To reduce the viscosity of the ink and improve the transferability of the ink, it is recommended to use the special 20# additive for gravure ink.
2 Adjust the position of the squeegee holder so that the distance between the squeegee and the plate cylinder is shortened.
3 Use a slow-drying solvent to reduce the ink drying rate and increase the dot gain.
4 Adjust the blade pressure and the print roller pressure.
5 Re-plate to change the shape and angle of the cell.
6 Change to a low viscosity ink.

Author: Wu

Reprinted from: Printing Technology