UV curing ink knowledge

Whether your company is just beginning to use UV inks or is planning to train new employees on UV technology, the information we provide can help you shorten the learning curve and receive good use and learning results.

1. What is the relationship between the setting parameters (watts/inch) on the UV curing lamp and the reading (watts/cm2 or milliwatts/cm2) we see on the radiometer?

Watts/inch is the power unit of the curing lamp. It is based on Ohm's law volt (voltage) x amps (current) = watts (power); and watts/cm2 or milliwatts/cm2 represents the passage of the radiometer. The peak illuminance (UV energy) in each unit area when curing the lamp.

The peak illumination mainly depends on the power of the curing lamp. The reason we use watts to measure the peak illuminance is mainly because it represents the power consumed by the curing lamps. In addition to the amount of electricity received by the curing unit, other factors that affect peak illumination include the conditions and geometry of the mirror, the useful life of the curing lamp, and the distance between the curing lamp and the cured surface.

2. What is the difference between milli-joules and milliwatts?

The total energy emitted to a particular surface over a period of time is usually expressed in coke/flat centimeters or millijoules/cm2. It is mainly related to the speed of the conveyor belt, the power of the curing lamp, the quantity, the service life, the state, and the shape and conditions of the mirror in the curing system.

The power of the radiant energy of UV energy radiated to a particular surface is mainly expressed in watts/cm 2 or milliwatts/cm 2 . The higher the UV energy that is irradiated to the surface of the substrate, the more energy is penetrated into the ink film. Whether it is milliwatts or millijoules, measurements can only be made when the wavelength sensitivity of the radiometer has reached a certain level.

3. How can we ensure proper curing of UV inks?

The curing of the ink film when it passes through the curing unit for the first time is very important. Proper curing minimizes the problems of distortion, over-cure, re-wetting, and under-curing of substrates, and optimizes the adhesion of inks and humour or coatings and coatings.

Screen printing plants must determine production parameters before production begins. In order to test the curing efficiency of UV inks, we can start printing at the lowest speed allowed by the substrate and cure the previously printed proofs. Subsequently, the power of the curing lamp is set to the value specified by the ink manufacturer. When dealing with hard-to-solid colors such as black and white, we can also properly adjust the parameters of the curing lamp.

After the sheet is cooled, we can use the bi-directional hatching method to measure the adhesion of the ink film. If the proofs pass the test, they can increase the speed of the paper by 10 ft/min before printing and testing until the ink film loses adhesion to the substrate. Record the belt speed and cure at this time. Lamp parameters. Then, depending on the characteristics of the ink system or the ink supplier's recommendations, the belt speed can be reduced by 20-30%.

4. If the colors do not overlap, should I care about over-curing?

The problem of over-curing occurs when the surface of an ink film absorbs excessive ultraviolet light. If you 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 do color overprinting, we don't have to worry too much about this issue.

However, we need to consider another important factor that is the printed film or substrate. UV light can affect the surface of most substrates and certain plastics that are sensitive to ultraviolet light of a specific wavelength. This sensitivity to specific wavelengths plus oxygen in the air can cause plastic surface degradation. The molecular bonds on the surface of the substrate may be damaged and cause the adhesion between the UV ink and the substrate to fail. The degradation of the substrate surface function is a gradual process and has a direct relationship with the ultraviolet light energy it receives.

5. What happens when the ink cures excessively?

There is a theory that when the surface of an ink is irradiated with excessive ultraviolet light, it becomes harder and harder. When people print another ink on this hardened ink film and perform the second drying, the adhesion between the upper ink and the lower ink becomes poor.

Another theory is that excessive curing can cause photo-oxidation on the ink surface. The occurrence of photo-oxidation destroys the chemical bonds on the surface of the ink film. If the molecular bonds on the surface of the ink film are deteriorated or damaged, the adhesion force between the ink film and another ink layer is reduced. Excessively cured ink film is not only less flexible, but it is also prone to surface embrittlement.

6, why some UV ink curing speed faster than other ink?

UV inks are generally formulated according to the characteristics of certain substrates and the specific requirements of certain applications. From a chemical point of view, the faster the ink cures, the less flexibility it has after curing. We can imagine that when the ink is cured, the ink molecules will cross-link reaction, if these molecules form a large number of molecular chains and there are many bifurcations, then the ink curing speed will be fast, but the flexibility is not high; If the molecular chain formed by these molecules is relatively small and there is no bifurcation, the curing speed of this ink may be very slow, but it will be very flexible.

Most inks are designed according to the application requirements. For example, for inks designed specifically for the production of membrane switches, the cured ink film must be compatible with the composite adhesive, but also have enough flexibility to adapt to subsequent processing such as die cutting and embossing. It is worth noting that the chemical materials used in the ink cannot react with the surface of the substrate, otherwise it will cause cracking or delamination. The curing speed of this ink is usually slow. The inks designed specifically for the production of cards or hard plastic panels do not require such high flexibility, and their drying speed is also faster depending on the application.

Whether the ink drying speed is fast or slow, we must start with the final application. Another notable problem is the curing equipment. Some inks can be cured quickly, but due to the low efficiency of the curing equipment, it may cause the ink to slow down or the curing is not complete.