Performance of UV cationic inks for thermal shrink film printing (2)

Self-based ink advantages

This device is fast. Radical ink curing is not too high temperature requirements, low-energy light source can be quickly cured, which greatly reduces the heat of the goods, avoid shrinkage of the heat shrink film in the printing process, and its requirements for ink composition Nor is it as harsh as cationic inks. In this way, a wide selection of pigments is sufficient to ensure that the ink has a good rheology on the YAG anilox roll. In addition, high pigment filling reduces ink volatility, reducing shrinkage and odor. Since the free radical ink has no restrictions on the choice of ingredients, it can print substrates that are more salty and can be printed in combination with alkali-soluble, water-soluble flexo inks.

The disadvantages of free radical ink

The free radical ink reacts quickly and quickly cures all components together, which increases the pressure on the substrate. When printing a heat-shrinkable film, excessive pressure and a small amount of heat energy of a curing UV lamp can cause shrinkage and deformation of the film. The shrinkage will also make the free radical UV ink soft as the same as other UV ink, the affinity, adhesion worse. Radical inks are also very susceptible to oxidation. However, this can be done with high-energy light sources, high-efficiency ingredients, or oxygen-absorbing initiators (eg, 2.4, diamines, and triamines). To illustrate, this is an experimental result obtained under conditions where the air conditions are relatively stable and there are no significant fluctuations. If it is used in actual production, it needs further demonstration.

new technology

The low ink film shrinkage and good flexibility make the free radical ink suitable for printing high shrinkage films.

speed

Drying fast. High adhesion allows radical inks to instantly adhere to the substrate and rapidly cure under low energy light; in this process, the substrate is not exposed to heat. Cationic inks, however, are unable to print at high speed due to high energy requirements for curing. This precisely solves the problem of UV flexo productivity lower than gravure. With proper curing equipment and pressure settings, free radical ink will break through this bottleneck.

shrink

This new ink quickly combines with the substrate. Due to the excessive speed, the ink film itself generates internal stress, but it is not enough to make it break. This internal stress is the same as the formation of the shrink film. The film cools after preheating and stretching, and the film retains the tension and memory tensile stress inside the film. When reheated, the disorientation occurs and the curl returns to its original state. The free radical ink ink film also has such helium memory tensile stress." When the shrink film print is heated, this feature is incomparable with gravure and aqueous flexo inks. Therefore, the use of this new technology and high shrinkage PETG materials in the shrink sleeve label market has reached 75%.

Graphic quality

The print quality of this new type of ink is better than the quality of the flexo printing with a 150 - 175 LPI photosensitive resin plate. The amount of ink used in this ink is half that of the gravure ink. Different from gravure printing with low viscosity ink and double ink layer thickness to achieve high quality dot reproduction, this new type of flexo ink is quickly cured with thin ink layers and brightly colored dots to obtain the same quality as gravure printing. Text. Opaque white can also do a very good opacity, can be used in conjunction with water-based ink to make up for the lack of water-based ink at this point.

cost

The cost of flexo printing is lower than that of gravure printing. In terms of printing, the photosensitive resin plate - engraved gravure cylinder, no solvent recovery device, low environmental requirements for UV lamp drying - traditional sleeve dryer. In addition, the flexographic version has a relatively low labor intensity, and long and short prints can be converted quickly. However, if you think carefully, you will find that the price of the selected pigment for UV ink is twice that of gravure ink. In this way, the two printing costs are not much different.

Curing concept

If you want to fundamentally solve the problem of shrinking <except ink properties> during printing, it is necessary to avoid shrinkage of the printing material by the UV lamp during curing. There are many methods, but none are suitable for thin film printing and solving the heat generated by the printing pressure.

Cooling roller

The cooling roller is the best choice for cooling and high-speed printing shrinkage. Although there are some other solutions, they have the problems of low speed and high waste volume.

Low-energy light source

We must then ensure that the ink film is firmly bonded to the substrate and that it has good expressiveness. Of course, the ink should not be over cured. Therefore, it is not possible to use the same light source for all color inks. The light drying time for light-colored inks is a bit longer, and some inks themselves can fully absorb the heat of UV lamps, such as carbon black ink, so no cooling is required. Adding a thin black ink layer before the four-color printing can effectively absorb heat and get a bright, dense black color. This is a very effective method.

Doped light source

The doped light source is a low-energy light source that provides sufficient curing energy. This is a good choice for high-speed operation of UV devices.

The use of a thermometer

The thermometer can accurately give you the current energy ratio of your working status. If not, you can control the temperature by comparing the UV thermochromic ink with the color ladder.

Cold UV ink

The light source system is the driving force behind this new technology. Dichroic mirrors, cold mirrors, and infrared filters reflect and filter light sources, leaving usable light. This new professional light source has been applied in the sleeve type heat shrinkable film printing industry. This low-energy light source can provide the complete curing energy of the ink, realizing low-energy, high-speed printing.

Conclusion The application of sleeve type heat shrink film is both a challenge and an opportunity for UV printing. With the continuous development of various technologies, special free radical UV devices have been able to get the ideal heat shrinkable film printing effect, accelerating the pace of the industrial development of shrink sleeves. Low-cost, good expressiveness has also brought free radical UV technology to the forefront of trends.


Long Chen Printing Technology Network