How to solve the problem of printing ink drying?

In printing, the problem of poor ink drying or too fast ink drying often occurs

01 The ink layer is too thick

In the process of large-area solid printing, the ink layer on the surface of the printed product is completely dried and the bottom layer is not completely dried during the drying process due to the large amount of ink and the thick ink layer, that is, the phenomenon of false drying

Solution

For jobs that use spot color UV ink to print on the ground, try to match the color of the spot color UV ink as darker as possible, so that during the printing process, the ink bottom layer can be completely dried by deep ink thin printing to increase its contact The bonding fastness of the substrate surface

02 Insufficient UV lamp power

Insufficient UV lamp power is also one of the reasons for the failure of UV ink drying, which is related to the daily production operations of the company, mainly in the following aspects:

1.

2.

3.

4.

Solution

First of all, a complete and effective UV lamp use management system must be established to ensure that the UV lamps work within the effective service life, promptly replace the UV lamps that have exceeded the service life, and pay attention to the use of UV lamps for the units that have replaced the UV lamps.

03 The ink is beyond the shelf life or the additives are excessive

In general, if the ink shelf life is exceeded, the photoinitiator in the ink may fail after printing, resulting in poor ink drying
.
In addition, in printing production, in order to improve the performance of the ink, it is often necessary to add additives such as varnish and detackifier to the ink
.
If the proportion of additives is too high, it may cause the ink to be too thin and cause poor drying
.
UV ink itself has thixotropy, that is, it becomes thinner and thinner under the action of the shearing force of the ink roller
.
Moreover, after the printing equipment has been running for a period of time, the ink rollers will generate heat due to friction, thereby reducing the viscosity of the ink
.

Solution

First of all, ensure that the ink is used within its shelf life; secondly, pay attention to the amount of ink auxiliary and desiccant.
It is recommended that the proportion of UV ink additives should not exceed 3% in summer and 8% in winter
.

04 Different colors of UV inks have different drying degrees

Tests have shown that UV inks of different colors have different absorption of the spectrum, so under the same power UV lamp, the drying degree of different colors of UV inks is different
.
For example, white UV ink can directly reflect light, black UV ink will diffusely reflect light, and magenta UV ink has a better light absorption effect
.

According to experience, the difficulty of drying the four primary colors of UV inks is black, cyan, yellow and magenta in order from difficult to easy.
Gold and silver UV inks are more difficult to dry than four primary colors of UV inks.
White UV inks reflect light.
The effect is also difficult to dry
.

Solution

According to the drying characteristics of different colors of UV inks, the printing color sequence should be arranged reasonably.
The inks that are more difficult to dry are printed first, and then the inks that are easier to dry are printed.
This can solve the problem of poor ink drying to a certain extent
.

05 The rubber roller density is too low

In actual production, new equipment is more prone to ink drying failure
.
After careful inspection, it was found that it was because the rubber roller with too low density absorbed the photoinitiator in the UV ink, which caused the ink to dry badly
.

The drying of UV ink is mainly achieved by the chemical reaction between the photoinitiator and the resin.
Among them, the molecular structure of the resin is larger, and the molecular structure of the photoinitiator is smaller
.
If the rubber roller density is too low, many small holes will appear on its surface.
Because the diameter of these small holes is larger than the diameter of the photoinitiator, part of the photoinitiator in the UV ink will be absorbed by the rubber roller, causing the UV ink to dry During the process, the chemical reaction between the resin and the photoinitiator was insufficient, resulting in poor drying of the ink, and at the same time, the phenomenon of ink drying on the surface of the rubber roller
.

Solution

The easiest way is to replace the rubber roller; if it is too late to replace the rubber roller, you can also remove the rubber roller and soak it in UV varnish for 12 to 24 hours.
At this time, the rubber roller will gradually absorb the UV varnish.
After being saturated, it is difficult to absorb the photoinitiator in the UV ink
.

06 Other reasons

The bright resin ink used in lithographic printing, under normal circumstances, the print transferred to the paper by the blanket can usually be dried within a few hours
.
However, in daily production, it is often encountered that the blot is too slow to dry, so the following reasons need to be investigated:

1.
Too much water supply?

2.
The pH of the fountain solution is too low?

3.
The temperature in the printing workshop is too low or the humidity is too high?

4.
Poor absorption of paper?

Solution

When the above problems occur, we must strictly control the size of the water on the page and master the pH value of the fountain solution
.
When the print is not dry, you should open the print in time to ventilate the paper so that air can enter the paper to speed up the conjunctival time
.

07 The ink dries too fast

When printing on a single-color offset press, the print of the previous color is often dried too fast, forming "crystallization", making the next color not overprinted.
The main reason is that the dry oil is added too much or the semi-finished product is stacked for too long.
This phenomenon is again It often happens when the yellow plate is printed or the light background is full
.

Solution

If this problem occurs, if the number of products that cannot be overprinted is small, you can use a clean soft cloth dipped in magnesium carbonate powder, and gently wipe the surface of each printed product to make the surface rough; use infrared rays to irradiate the ink layer to heat and expand.
Coarse; if the quantity is large, the humidity can be treated to make the ink layer swell and swell, and the surface will be roughened
.

After the surface of the ink layer becomes thicker, the latter color ink is easy to adhere.
In order to prevent the phenomenon of not being printed, you can add an appropriate amount of non-drying wax auxiliary agent to the yellow ink in advance to prevent the ink layer from crystallizing.
When the color is full, you can mix the Villi oil and the thinner to prevent the latter color from not being printed
.