10 reasons and countermeasures for poor ink transfer

Gravure printing is a very important one of the traditional printing methods (lithography, letterpress, gravure, screen printing), and it occupies an important position in aluminum foil printing for pharmaceutical packaging and plastic flexible packaging printing

★ Principle of gravure printing

In the printing process, the manuscripts to be copied are divided into text line manuscripts and halftone manuscripts with gradation changes

★ Factors affecting the transfer volume of gravure ink

Looking at the printing process from the perspective of ink, printing is actually a transfer process of ink from the printing plate to the substrate

1.

Cells are formed mainly by chemical etching or electromechanical engraving.

2.

The finer the ink particles, the more ink particles that enter the printing grid, and thus the greater the transfer volume

3.

The viscosity of the ink is also very important in the ink transfer process.

4.

The greater the angle of the doctor blade, the greater the pressure, and the more ink in the cells is scraped off, thereby reducing the amount of ink transfer

5.
Printing speed

The faster the speed, the greater the amount of ink transfer
.
There are two reasons: one is that the drying time of the ink in the cell is shortened before transfer, and the viscosity does not change much; the second is that the amount of ink in the cell increases when the pressure of the squeegee remains unchanged, thereby increasing the transfer volume
.
Therefore, the printing speed should be increased as much as possible while the printing quality can be guaranteed
.
The printing speed of flexible packaging compound is generally 120-250m/min
.

6.
Solvent volatilization speed

There are three solvent formulas with different volatilization speeds: fast drying, standard drying and slow drying, which are generally provided by ink factories
.
If the solvent volatilizes too fast, the viscosity of the ink in the ink tray will increase.
At the same time, more importantly, the viscosity of the ink in the cell will rise sharply before the transfer.
If it dries up in the cell, the transfer volume will decrease significantly.
In severe cases, there will be leakage failure.

.
Therefore, in general, to increase the ink transfer rate, especially when printing shallow-level patterns, slow-drying solvents should be used
.

7.
Electrostatic ink absorption auxiliary device

The actual transfer rate of the ink is only about 60%, and the ink in the small cells is difficult to transfer because it is not easy to form capillaries
.
With the extension of printing time, the leakage phenomenon becomes more obvious
.
The electrostatic ink absorption device uses the electric field force to help the ink in the cell transfer to the substrate, which can increase the transfer rate by 10%-20%, especially in the printing of small dots, the improvement phenomenon is more obvious
.

8.
Press roller pressure

The function of the pressure roller is to help form "capillaries" between the substrate and the plate roller, so that the ink is transferred to the substrate along the "vessels"
.
The pressure is not the greater the better, the pressure is greater, the substrate is more difficult to drive, which affects the accuracy of overprinting
.
Therefore, in printing practice, the pressure setting principle is to ensure the printing effect as small as possible
.

9.
The surface tension, flatness and smoothness of the substrate

The surface tension of the substrate is generally 1.
2X10-4N larger than the surface tension of the ink, so that the capillary action will be formed with the help of the pressure roller, allowing the ink to transfer from the printing plate to the surface of the substrate
.
The greater the surface tension, the greater the amount of transfer
.
For example, under the same printing conditions, plastic film NY, PET and BOPP are printed

The transfer rate of brush ink is gradually reduced, because the surface tension of their printing surface is also gradually reduced (of course, they all meet the printing requirements: the surface tension is greater than 0.
04N/m)
.
The flatness and smoothness of the film surface are very good, while the flatness and smoothness of the paper surface are different due to different paper types
.
The better the flatness and the higher the smoothness of the substrate, the greater the amount of ink transfer during printing
.

10.
Environmental impact: temperature, humidity, granularity

Generally, the ink fluidity is good when the temperature is 20-25°C, and the printing effect is better
.
The higher the temperature, the faster the volatilization of the solvent in the ink, the higher the viscosity of the ink, and the destruction of the ink solvent balance; if the temperature is very low, the fluidity of the ink will be reduced, thereby affecting the ink transfer
.

When the humidity is high, water vapor will condense on the plate roller, causing condensation on the surface of the plate roller, and production is impossible.
At the same time, the water vapor condenses into the ink, which will destroy the quality of the ink; low humidity, dry air, easy to form static electricity, easy to form electrostatic burrs on the edge of the printing pattern
.

There is a lot of dust in the air in the printing workshop, which is easy to make the guide roller and the pressure roller dirty, and the impurity particles on the guide roller and pressure roller converge to a large amount, which may cause irregular printing patterns to form
.