UV-CURING INK COMMON PROBLEMS

What happens when the UV ink is over-cured?

One theory is that when the ink surface is exposed to too much ultraviolet light, it becomes harder and harder. And when people in this layer of hardened ink film to print an ink, and a second drying, the adhesion between the upper ink and the lower ink will become very poor. Over-curing ink film not only poor flexibility, but also prone to surface embrittlement.

Why do some UV inks cure faster than other inks?

UV ink is generally based on some of the characteristics of the substrate and some applications of special requirements and preparation. From a chemical point of view, the faster the curing rate of ink, the worse its flexibility after curing. Ink used in the chemical raw materials can not react with the substrate surface, otherwise it will cause cracking, crushing or delamination and other phenomena. This kind of ink curing speed is usually relatively slow. Inks designed for the production of cards or hard plastic display boards do not need to be so flexible, and they dry faster depending on the application. Most inks are designed according to application requirements.

Why does the polycarbonate (PC) film turn yellow when I use UV ink?

Polycarbonate is sensitive to ultraviolet light with wavelengths less than 320 nanometers. The yellowing of the film surface is caused by the breakage of molecular chains caused by photooxidation. Plastic molecular bonds absorb ultraviolet light energy and produce free radicals, which react with oxygen in the air to change the plastic's appearance and physical properties.

How to avoid or eliminate polycarbonate surface yellowing?

If UV ink is used to print on polycarbonate film, its surface yellowing can be reduced, but not completely eliminated. This yellowing can be reduced by using solidified bulbs with added iron or gallium. In addition, the proper curing of each ink color also helps to reduce the exposure time of the substrate to UV light and the possibility of discoloration of the polycarbonate film.

How do we ensure proper curing of UV ink?

The curing of the ink film is very important when it first passes through the curing unit. Proper curing can minimize the deformation of the substrate, over curing, rewetting and undercuring problems, and can optimize the stickiness between ink and ink or coating and coating.

In order to test the curing efficiency of UV ink, we can start printing at the minimum speed that the substrate can allow, and solidify the pre-printed proofs. Subsequently, the power of the curing lamp is set to the value specified by the ink manufacturer. And in the black and white and other difficult to cure the color processing, we can also appropriately adjust the parameters of the curing lamp.

If the colors do not overlap, should we be concerned about the problem of over-curing?

When the surface of an ink film absorbs too much ultraviolet light, there will be excessive curing problems. If we cannot find a solution to this problem in time, the surface of the ink film will become harder and harder. Of course, as long as we don't overprint in color, we don't have to worry too much about this problem.

However, we need to take into account another important factor, that is the film or substrate to be printed. Ultraviolet light can affect most substrate surfaces and some plastics that are sensitive to ultraviolet light at certain wavelengths. This sensitivity to specific wavelengths combined with oxygen in the air can cause degradation of the plastic surface. The molecular bond on the substrate surface may be destroyed, and lead to the failure of adhesion between UV ink and substrate.

The degradation of substrate surface function is a gradual process, and its received UV energy has a direct relationship.

UV ink is green ink, why?

Compared with solvent - based ink, UV ink is more environmental protection. UV ink can become 100% solid, which means that all the components in the ink will become the final ink film.

How does plasticizer affect the adhesion of ink on PVC?

Plasticizers are chemicals that make printed materials softer and more flexible, and are commonly used in PVC (polyvinyl chloride). The type and amount of plasticizer added to flexible PVC or other plastics depends on the mechanical, heat and electrical properties of the printed material.

Plasticizer may migrate to the substrate surface, and affect the adhesion of ink. Residue on the surface of the substrate plasticizer is a pollution, will reduce the surface energy of the substrate. The more pollution on the surface, the lower the surface energy, its adhesion to the ink will be smaller. To avoid this, people can improve their printability by cleaning the substrate with a mild cleaning solvent prior to printing.

How does the viscosity of the ink affect printability?

Most inks are thixotropic, which means that their viscosity changes with time and temperature. In addition, the higher the ambient temperature, the lower the viscosity of the ink. Screen printing inks generally work well on printing presses, but there are occasional problems with printing suitability depending on press Settings and prepress adjustments. And the viscosity of the ink on the printer is different from the viscosity in the cartridge.

Ink manufacturers will set a specific viscosity range for their products. For too thin or too low viscosity ink, users can also be appropriate to add thickener; For too thick or too high viscosity ink, users can also add thinner. In addition, you can also contact ink suppliers, ask for product information.

What are the factors that affect the stability or shelf life of UV ink?

An important factor affecting the stability of ink is the storage of ink. UV ink is usually stored in plastic cartridges rather than metal cartridges, because the plastic container has a certain oxygen permeability, which ensures a certain air gap between the ink surface and the container lid. This air gap -- especially the oxygen in the air -- helps to minimize premature ink crosslinking.

In addition to packaging, the temperature of the ink container also plays a vital role in maintaining their stability. High temperature will cause the advance reaction of ink and crosslinking. The adjustment of the original ink formula may also affect the stability of the ink on the shelf. Additives, especially catalysts and photoinitiators, may shorten the shelf life of ink.

If you use nitrogen curing unit to cure color UV ink, what will happen?

Curing systems that use nitrogen to cure printed matter have been around for more than a decade. These systems are mainly used in the curing process of textiles and film switches. People want to use nitrogen instead of oxygen, mainly because oxygen will inhibit ink curing.

However, because the light bulb in these systems is very limited, the curing effect of pigments or colored inks is not very good.