1. What is the UV curing principle?

 

  UV curing means that the photoinitiator absorbs the radiant energy of the ultraviolet light and then splits into free radicals under the irradiation of ultraviolet light, causing the prepolymer to undergo polymerization, cross-linking, and grafting reactions, and cures into a network in a very short time. Polymers. As a result, UV coatings, inks, adhesives, and the like are converted from a liquid state to a solid state in a matter of seconds to form a cured film.

 

  The UV curing process can generally be divided into the following five stages.

 

  (1) The photoinitiator absorbs ultraviolet light and becomes an excited photoinitiator.

 

  (2) The excited photoinitiator is unstable and easily decomposes to form free radicals.

 

  (3) Free radicals interact with unsaturated groups in the prepolymer to initiate addition, cross-linking, or polymerization reactions to form free-radical intermediates.

 

  (4) The radical intermediates are long chain or network-like macromolecular polymer radical intermediates through a chain growth reaction.

 

  (5) Long-chain or net-like polymer radical intermediates produce a chain termination reaction, and the original liquid component is converted into a solid polymer.

 

  2. What are the influencing factors of UV curing?

 

  The main factors influencing the UV curing reaction are: the emission spectrum and the radiation intensity of the UV lamp in the UV curing device, and the absorption spectrum of the photoinitiator in the UV ink, the paint or the adhesive, and the formulation and composition thereof.

 

  In the UV curing reaction, it is most important to determine whether the UV light emitting spectrum in the UV curing device matches the absorption spectrum of the photoinitiator in the UV ink, paint, or adhesive. If the two do not match, then the photoinitiator can not be excited, the UV curing reaction will not be able to be completed successfully; if the two are not completely matched, the UV curing reaction will easily lead to incomplete; if the two match, then the curing effect and UV The radiation intensity of the light source is directly related. In addition to spectral matching issues, the choice of UV curing equipment, UV inks, coatings, and adhesives in the curing reaction must also take into account the effects of surface curing and deep curing in order to achieve different application requirements.

 

  In general, UV curing uses a high-pressure mercury lamp as a curing light source (note that the quality and lifetime of the UV lamp directly affect the degree of UV curing reaction). Of course, according to different requirements, lamps with different additives (such as iron lamps, xenon lamps, etc.) can also be selected to change the output spectrum of the UV lamp to meet specific curing requirements. In general, high UV light source radiation intensity can increase the surface curing and deep curing effects of UV inks, coatings, and adhesives.

 

  3. How to reduce the generation of special odors in UV curing?

 

  The odor emitted by UV curing is the decomposition product of photoinitiators, such as benzaldehyde or thiol, which have special odors. We know that in the UV curing reaction, nitrogen is often used as a shielding gas to reduce the influence of oxygen and water vapor on the UV curing reaction (oxygen and water vapor can participate in the UV curing reaction, depleting the energy of the UV light source, and generating ozone ). In addition, the UV curing reaction under nitrogen protection conditions, the amount of photoinitiator is only 1/5 of the conventional curing conditions. As the amount of photoinitiator is decreased, the amount of benzaldehyde or mercaptan that is decomposed by it will also decrease, and the odor in the UV curing reaction will also be relatively small.

 

  It can be seen that the use of nitrogen protection can reduce the generation of special odors to a certain extent, and a more effective solution to the problem of special odors generated during UV curing is to select polymerizable photoinitiators or photoinitiators with large molecular weights. Reduce the volatility of its decomposition product benzaldehyde or thiol.