Technical characteristics of oil-based and UV-cured inks

Editor's note: In the past, when we used offset printing on plastic films, we used mainly mineral oil-based binders. However, with the increase in ink performance requirements of printing plants, product processing plants and end-users, UV inks have gradually replaced oil-based inks. In this article, we will introduce the current situation and technological innovation of these two types of ink systems in detail.

At present, synthetic materials such as plastic films and other non-absorbent substrates are used more and more frequently in the printing field, especially offset printing. If we want to find a suitable offset ink system for these applications, we must make the system have the following characteristics:

Good printability

Better operating characteristics on high-speed printing presses

Adhesion and scratch resistance on non-absorbent substrates

Unlike most paper and paperboard substrates, the surface structure of the plastic film does not permit ink penetration, and it is even less likely that the ink will dry quickly. In addition, the fountain solution used in stencil offset printing also affects the drying process of oil-based inks. Therefore, a good ink balance is a key factor affecting the drying process. For this reason, people have specially developed oil-based inks for the synthesis of substrates, which can not only meet special technical requirements, but also ensure the printing quality of products. However, compromises between performances such as rapid drying, safe stacking, adhesion, and abrasion resistance are still a challenge for oil-based inks.

The characteristics of UV curing technology can just make up for the shortcomings of the above-mentioned problems of oil-based inks: its ink film can be cured in time, and it is almost unaffected by the amount of fountain solution, and it can be quickly prepared for subsequent processing.

Upgraded UV curing ink

When the UV ink system was first introduced into the printing industry, it was often questioned by the poor performance and adhesion problems on offset presses. But now, by improving ink formulations and using new raw materials, people have successfully eliminated the drawbacks of traditional UV inks.

Printability of UV inks

For non-absorbent substrates such as plastic films, the fountain solution cannot penetrate the surface of the substrate at all. Therefore, the first-generation UV ink can easily accumulate on rollers, plates, and blankets, causing serious quality problems. At this time, we need to rely on the ideal ink balance to improve the printability of the ink. The new generation of UV ink has a stronger absorption, and provides a greater use of fountain solution.

In recent years, non-alcohol printing has shown a growing trend. Especially in the printing of films and foils, isopropyl alcohol (alcohol) has become an ideal choice for people. It can reduce the surface of the fountain solution. Tension optimizes the printing process so that the printing system achieves the desired ink-water balance. In addition, people can use other alcohol substitutes to moisten printing units and plates.

UV ink adhesion

In the past, UV inks were difficult to attach to metal foils and film surfaces, and these problems have now been effectively solved by developing special components and optimizing ink formulations.

However, there is a prerequisite for the use of UV inks, that is, such as PVC substrate can not contain plasticizers, electrostatic inhibitors and other components that may reduce the adhesion of ink.

The surface tension of PVC is preferably kept at about 35 mN/m. For substrates made of ABS, PP, PET, PE, and PS, the surface tension should be at least 40 mN/m. In addition, these substrates should not contain additives such as electrostatic inhibitors to prevent their groups from interfering with the even distribution of ink adhesion. The surface tension of synthetic materials depends mainly on the formulation and manufacturer of the material. Ink manufacturers sometimes treat the film surface with a flicker discharge technique. As the storage time increases, the surface tension of the substrate will decrease, and the corona discharge pretreatment must be repeated directly on a web or sheet-fed press. Of course, this method also applies to substrates that have not been pretreated.

UV cured ink film flexibility

UV inks and coatings can easily shrink during curing. The thicker the ink film or coating, the greater their shrinkage. The result is a drop in ink adhesion. The adhesion of inks is directly related to the use of highly flexible inks, coatings, and binders because they help reduce the degree of ink shrinkage.

UV ink curing

Different curing characteristics can affect the ink/coating adhesion. If the ink does not completely cure, their adhesion will inevitably weaken. In rare cases, excessively dry ink/coating layers may also suffer from severe shrinkage and eventually reduce flexibility and flexibility.

UV ink functionality

In the early days of UV technology, it was almost impossible for people to use them for printing on films and foils. Today, improvements in quality and performance have enabled us to perform UV film printing on more paper substrates.

Requirements for UV systems

The cold UV system can reduce the amount of heat generated by the discharge and the temperature of the stack, and place distortions in the film and foil. However, it also slows down the polymerization of UV inks and coatings. If nitrogen is added during the reaction of the ink, the cross-linking polymerization speed of the cells will be accelerated, and it will bring us higher production speed. For every print job, we have to test the adhesion of the ink and coating. Unlike scratch resistance, ink adhesion generally does not change much within 12 hours of printing.

to sum up

With the ever-expanding choice of substrates that consumers can choose - from plastic films to metal substrates, ink manufacturers are constantly improving their products. In addition, the increase in the speed of the printing press and the shortening of the drying time have also posed severe challenges to us.

Due to the successful resolution of heat shrinkage problems, oil-based inks will also find application in many special areas. However, UV inks are not to be outdone. They will improve formulas, enhance color control in the prepress stage, and dry the equipment. Features to constantly expand their market scope in the field of printing.