Scientific research on film forming principle of UV-curable waterborne coatings. The research on the film forming principle of DW coatings is particularly important for water-based UV-curable coatings. Only by making clear all the curing film forming process can we select and synthesize the main resin, initiator and emulsifier, and find the theoretical basis source.

After the UV curable water-based latex is dried in the vacuum dryer, although the photoinitiator is fixed in the film, the cross-linking reaction still occurs when UV irradiation. TomScherzer et al. used near infrared reflectometry to detect the conversion rate of the double bond and monitor the UV curable process and quality of the acrylic coating online. If a low-power ultraviolet lamp can be used to slow down the curing film formation process, and then use a combined analyzer to photograph the microscopic process of all curing film formation, it is more convenient to study.

Develop water-based coatings that can be cured directly by ultraviolet light without pre-heating. Water-based UV-curable coatings generally must be baked before UV-curable to speed up the evaporation of water, and even the original UV-curable electrophoretic coating must have a "flash" process to remove excess water. This makes the whole curing process of water-based coatings complicated and energy consumption increased. In addition, after ultraviolet curable water-based coatings undergo infrared drying, the photoinitiator has long been fixed in the coating, at this time, through ultraviolet light irradiation, a further reaction crosslinking, will produce internal stress, so that the coating performance is affected. The method of first light curing and then heat curing is used to make the stress subside and the coating with relatively high thermal stability is produced. However, the coating itself is a poor conductor of heat, the heat released by the polymerization reaction will make its temperature rise, and the generally used ultraviolet light source has a considerable amount of infrared radiation, it can be used to make water evaporation and reaction curing at the same time. There are two ways to do this, one is to increase the solid content and reduce the time of water evaporation in the early stage. The synthesis of high solid content and low viscosity (PMMA/BA/AA) latex with 72% solid content is equivalent to directly entering the middle stage of film formation. The second is the introduction of Hyperbranchedpolymer (hyperbranched polymer) to make the reaction more rapid and shorten the curing film formation time. Moreover, the hyperbranched polymer has a demulsification effect, after which water and emulsifier will float to the surface of the resin, which is equivalent to accelerating the evaporation of water. AnilaAsif et al introduced water-soluble multi-functional superdendritic polyester into polyurethane acrylate emulsion polymer, which reduced resin viscosity and increased curing rate. For the workpiece with complex shape, it is difficult to cure in the place where the ultraviolet light is not direct, and the current research can be double-curable UV-curable water-based coatings, because the resin needs to add two initiators (such as photoinitiator and thermal initiator) at the same time, so the development of the coating formula is too complicated. For latex with a molecular weight of more than one million, it can be naturally dried or heated to form a film, which is equivalent to double curing.

Polymer prepolymers containing multiple functional groups were synthesized. Traditional solvent-free photocurable coatings are difficult to combine high hardness and high flexibility, in contrast, UV-curable water-based coatings can use a water-based dispersion system of polymer materials, and its viscosity is irrelevant to the relative molecular mass of the polymer, which solves the contradiction between high hardness and high flexibility of the photocurable coatings from the source. The cross-linked emulsion has better water resistance, alkali resistance, boiling water resistance and moisture resistance than the emulsion without functional group. The combination of reactive emulsion and water-soluble polymer to make coating is one of the directions of industrial coating. However, there are still many difficulties in how to introduce multifunctional groups into polymer emulsions with millions of molecular weight, because the polymer is surrounded by emulsifiers. JOHANODEBERG et al. have synthesized latex macromolecules containing unsaturated functional groups, so that other multi-functional monomers do not need to be added when UV curing film is formed. In the relevant literature, functional groups were introduced in the process of emulsion polymerization, and after the reaction, the film with cross-linked structure was obtained. If you can develop an emulsifier with functional groups such as carbon-carbon double bonds, so that the emulsifier can also participate in the reaction, it will be more perfect.

Nano color pastes and fillers. Ultraviolet curing coatings are generally made of varnish, because the paste and filler have a refraction effect on ultraviolet light, so that the deep curing of the film is hindered, but in many cases, the paste is also necessary, for example, in an important application field of ultraviolet curing fiber coating, you need to use different colors of paint to mark the type of fiber. Nanoscale pigments and fillers generally have better light transmission and should be hopefully used in UV-curable water-based coatings. Nano titanium dioxide was introduced into latex production. When nano silicon carbide is introduced into UV-curable resin, there is interaction force between the nano material and the matrix resin, and it is uniformly dispersed in the matrix resin. Compared with matrix resin, the physical properties of nano-composite resin are changed.

Alcohol-soluble UV curing coating. The UV-curable coatings using ethanol instead of water as solvent have not been reported in the references, but have been used in actual industrial production. In most cases, ethanol is used as a co-solvent, using a mixture of water/alcohol (volume ratio 80:20), resulting in a great improvement in the flexibility of UV-curable epoxy-acrylate films, and little impact on other properties. Because the preparation of water-based UV-curable coatings must be carried out in the process of preparing water-based resins, and the molecular weight of solvent-free UV-curable coatings cannot be prepared too high (it is generally believed that the molecular weight is above 100,000, it is already solid). Alcohol-soluble UV-curable coatings combine the advantages of both, and ethanol as a solvent itself is also very environmentally friendly, because ethanol surface tension is smaller than water, the wettability of the base material is strong, and the oil on the base material is dissolved, so it can obtain a coating with good adhesion.