The role and characteristics of active monomers in UV glue
2021-07-08 3127
1. In UV adhesive, active monomers, photoinitiators, oligomers, etc. are one of the main factors determining the curing rate of the system;
2. Active monomers connect high molecular weight oligomer molecules together, and relying on their functionality, they usually make a significant contribution to accelerating complete curing. Active monomers with bifunctional, trifunctional, and more functional groups are prone to forming cross-linked networks;
3. Active monomers affect or improve the performance of cured coatings. When oligomers and other components are the same, using different monomers may result in different performance and curing rates. When selecting active diluent monomers for a certain purpose, the following properties need to be considered: viscosity, dilution ability, solubility, volatility, flash point, odor, toxicological properties, activity to ultraviolet light, functionality, glass transition temperature of homopolymers and copolymers, percentage shrinkage during polymerization, and surface tension.
4. Low viscosity, dilution ability, and solubility: In UV glue, one of the main functions of monomers is to reduce viscosity. If the monomer has a strong ability to reduce viscosity, its dosage can be minimized. This can maximize the impact of the main oligomers of the material on the properties of the cured material. It should be pointed out that low viscosity active diluents may not necessarily have a strong ability to reduce viscosity.
5. Volatility, flash point, and odor: Diluting monomers with single functional group activity is more important. Due to their low molecular weight, they are often volatile materials with low flash points and strong odors.
6. Toxicity: This is a factor that must be considered when selecting UV adhesive monomers. Acrylates, which are volatile organic compounds (VOCs), are mostly irritating and toxic, making UV curing technology still unable to eliminate environmental pollution.
7. Activity, functionality, and polymerization shrinkage rate: They have a significant impact on the properties of materials, such as curing rate, flexibility, hardness, durability, and adhesion to various substrates. During the polymerization reaction, the coating density increases with the consumption of double bonds, resulting in total volume shrinkage. This shrinkage may be very severe (up to 20% when using certain monomers), which can have a significant impact on the properties of the coating.
8. Glass transition temperature (Tg) of polymers: For certain applications, Tg may be an important indicator. As for whether the desired Tg of the obtained material is high or low, it depends on the purpose. For example, for both fiber optic coatings, it is desired that the Tg of the inner layer coating be very low to achieve better flexibility; And the outer layer hopes to have a higher Tg to have better mechanical and chemical resistance performance.
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