Comparison of properties of EB varnish and UV varnish in post-printing process (2)

　 EB Varnish and UV Varnish Performance Differences

1. The difference between drying (curing) principle and equipment

UV Varnish is based on an initiator in varnish that absorbs UV light, generates free radicals, initiates the reaction of monomers and oligomers, and cures. A homemade laboratory curing equipment 20,000 RMB to domestic production facilities of about 200,000 to 300,000 RMB.

EB Varnish is under the intense bombardment of an electron beam, and the double bond on the monomer and oligomer is forcibly opened, generating free radicals and completing the polymerization. An imported laboratory EB curing device needs about 10-20 million dollars, while the production equipment is between 50-80 million dollars.

At present, the core technology of EB curing equipment is in the hands of a few foreign companies. Due to the small volume production of such equipment, the price is high. It is believed that if the technology is used universally, a reasonable price should be between 30-50 million US dollars. If the manufacturing technology of the device is mastered by Taiwan or domestic counterparts, it is believed that the price will be lower.

2. The difference in smell

Both UV oils and EB oils do not contain solvents, so odor problems during construction do not exist. The so-called smell mainly refers to the residual odor on the printed surface. There are two sources of residual odors in UV oils: residual initiators and reactive monomers, and other small-molecule materials generated after the initiator reacts. The UV oil initiator is modified and the reaction is increased. The odor will improve, but it cannot be completely removed.

There is no initiator in EB varnish, and the degree of reaction exceeds 98% , so there will be no residual odor problems like UV oil.

3. The difference between yellowing resistance

We know that paper that has been treated with UV oil will gradually turn yellow after it has been left for a long time. The main reason is that residual initiator and initiator products absorb ultraviolet light, use expensive initiators or add UV absorbers to UV oils. It will help, but it will not be completely yellowed. EB Varnish does not use initiators, so this problem does not exist.

4. The problem of ink discoloration

The UV lamp generates infrared rays, and also generates infrared rays, which causes the surface temperature of the paper that has been painted to be high. Because the production efficiency must be ensured, the paper is piled together when the temperature is too low, and the paper in the inner layer will be 30- At a temperature of 60°C for a while, some inks with poor heat resistance will change color. In addition to the effect of temperature, initiators in UV oils still retain a certain level of activity at relatively high temperatures and may react chemically with some of the active materials in the ink. This is the reason UV inks cause ink discoloration. one. The improvement of UV lamps, reflectors, and cooling systems will solve the problem of ink discoloration to some extent, but it is also a solution to the problem.

In the curing process of EB varnish, the curing device does not generate infrared rays during the generation of the electron beam, and the temperature problem is well solved. Therefore, the e-beam curing is a real cold energy source and is more suitable for some heat-sensitive substrates.

5. Comparison of the degree of curing

In order to understand the degree of curing of UV and UV oils, the concept of gelation rate was introduced here. The method of determination was: Varnish was made into a coating film with a thickness of 100 μm . The cured coating film quality W0 was recorded with acetone. Extract for 48 hours and vacuum dry at 50°C for 8 hours. Record the extracted mass Wg. Then calculate as follows:

Gel rate = Wg/W0 x 100%

The higher the gelation rate, the higher the degree of curing. In any case, UV oils increase the energy, and the degree of curing is only about 75% . The normal construction energy of UV oils is 50-100mJ/cm2 , which means that the UV oils we use today have 25-30% of small molecules on the surface of prints. Substance residues, these small molecular substances, on the one hand to reduce the physical properties of the product, on the one hand there are serious security risks, if possible, can lead to human skin allergies.

The curing energy of EB varnish reaches 40kGy (expressing unit of electron beam energy), the curing degree can reach more than 98% , and the physical properties and safety are well solved.