UV inkjet printing technology application (3)

3 Effect of oxygen barriers

When UV inks are used for the combination of various hemispherical ink droplets, in particular when using radical UV inks, the degree of influence of oxygen inhibition is different, and it is difficult to deal with the ink alone. Taking FIG. 5 as an example, comparing the existence of the point alone on the substrate and the existence of the point coincidence, it can be seen that the surface area of ​​the ink alone exists. In the case of a free radical UV ink, it is consumed by oxygen before the free radicals react with the monomers, thereby slowing the cure.

S. Jonsson et al. studied the absorptivity of the ink film for a simplified proportional formula (Ia=constant.Io.epsilon.I., where Ia is the ink film absorption, Io is the incident light quantity, and phI is the photoinitiator content). The amount of Ia is fixed as a variable of the illuminance Io and the photoinitiator content phI. The thickness of the cured ink film for the experiment was 50 μm. The C=C conversion of the upper (25 μm) and lower (25 μm) layers of the ink film was measured using a Fourier transform infrared spectrophotometer (FTIR), and the direction along the depth of cure was determined. Curing characteristics?
In order to keep the amount of light absorption of the ink film fixed, two combinations of high-illumination UV irradiation + low photo initiator content and low-illumination UV irradiation + high photoinitiator content were used. The measurement results are shown in Figs. 4a and 4b. From the results of the combination test of the high-illumination UV irradiation and the low photoinitiator content shown in Fig. 4a, it can be seen that the ink film has a more uniform curing characteristic in the depth direction. UV ink jet applied to a non-ink-absorbing substrate, after the ink is deposited, the ink film forms a hemispherical, according to the printed pattern, the hemispherical dot density is not the same, the dot size and the ink film thickness is also different (Figure 5) ).

According to many studies in Europe and America, it has been proved that high-intensity UV lamps have a certain effect on the prevention of oxygen barriers.

● Luminous output stability and long life

The UV curing reaction is affected by the illumination illuminance, the emission spectrum, and the temperature at the time of the curing reaction. Irradiation using strong light and ensuring the stability of the light emission spectrum during use is an important factor. The key factors that guarantee the illumination illumination and the stability of the luminescence spectrum are the stability of the light-emitting light valve itself, the optical system, and the power supply that supplies energy to the light-emitting light valve.

● Cool air and low heat

In order to keep the surface temperature of the light valve constant, the surface of the UV system light valve must be cooled. Air cooling is used on most occasions.

It is important for UV inkjet systems that the cooling air must not be affected when the print head ejects ink in picoliters. The heat emitted by the lamp device is effective to promote the curing reaction, but it must not affect the print head. At the same time, a low-thermal UV lamp device should also be used for a base material that does not have heat resistance, or a base material that causes the moisture in the base material to evaporate due to heat to cause wrinkling.