UV CURABLE HYDROGEL COATINGS WITH CONTROLLED SWELLING BEHAVIOR
Based on our knowledge of UV curing chemistry and our coating expertise several UV curable hydrogel coatings have already been developed with a swelling capacity ranging from 300 to 600 times their own weight in water. The swelling capacity and the kinetics of the swelling process can be fine-tuned by changing the monomer composition and by choosing the right coating application. Parameters like adhesion, flexibility and the tackiness of the final hydrogel coating can also be addressed by using the right additives and processing techniques. Even a color can be added to the formulation so to make the coating (in dry and/or swollen state) visible for the eye.
Our hydrogel coatings are based on an innovative waterborne UV curable formulation, containing a dedicated selection of monomers and oligomers, in combination with a water compatible photo-initiating system (Patent: EP2835385A1).
The applied coating can be cured in a conventional UV-curing line. Due to the exothermic polymerization process only a small amount of water remains within the layer that can be removed by a quick additional drying step (air drying or IR drying).
Due to a smart selection of monomers and oligomers a highly functionalized water absorbing coating can be designed with respect to the requirements.
Figure 1: Illustration of the swelling capacity of a UV cured hydrogel sample by tuning the monomer composition and the degree of cross linking
BLOCKDROP: Focus on three functionalities:
The formulations that have been developed are commercialized under the brand name BlockDrop and lead to safe and ecofriendly coatings.
Depending on the application the BlockDrop formulation can be optimized towards different functionalities:
Water absorption: depending on the degree of cross-linking, the water absorption of the coating can be tuned between 10 to 500 times its own weight
Water blocking: during the water absorption process an osmotic pressure will be built up, resulting in water blocking properties
Controlled release: water soluble compounds could be integrated within the coating, to be released during the swelling process of the coating
BlockDrop is ChemStream’s alternative for the so called hydrogels. Instead of incorporating SAP-particles into coating formulations, which is currently the common procedure in the field, the BlockDrop coating is a water absorbing layer in itself. The principle is illustrated in figure 2 by comparing a swollen yarn that was coated with a SAP-particle-containing Plastisol, with an BlockDrop-coated yarn.
The BlockDrop product line is a non-hazardous waterborne coating formulation that leads to a UV-cured coating without releasing VOC’s (volatile organic components), avoiding the use of plasticizers (typically used in Plastisol coating) and that does not harm the aquatic life.
Figure 2: Comparison between a classical SAP coating and the ChemStream BlockDrop coating
Applications of these coatable and UV curable hydrogel formulations can be situated in the telecommunication sector as well as in the medical and hygienic sector, in fire protection and humidity control, for filtration purposes, in the horticulture sector, etc.
A benefit to the classical superabsorbing polymer powders (SAPs) that are frequently used in practice (f.e. in diapers, in water-blocking yarns, …) is the firmness of a coated hydrogel structure which can retain the water in the form of the applied coating.
The principle is illustrated by comparing a swollen yarn that was coated with a SAP-particle-containing Plastisol, with an BlockDrop-coated yarn
Figure 3: Comparison of a swollen PES-yarn coated with Plastisol containing SAP-particles (present manufacturing process) with a BlockDrop-coated yarn