A Guide for Engineers
Acrylate UV curable materials have become a staple in industries such as coatings, adhesives, and 3D printing due to their rapid curing characteristics and excellent properties. However, the utilization of these materials necessitates a clear understanding of their properties, particularly in the design and operation of dispensing systems. This paper provides an in-depth guide for design engineers, focusing on key factors for system design, scale-up considerations, and production use considerations.
To optimize system design for acrylate UV/EB curable systems, engineers must consider several crucial factors. Firstly, the dispensing system should be designed to reduce premature curing. Since curing is significantly influenced by heat and the lack of dissolved oxygen, pumps inducing less shear and pressure are generally favorable. However, with appropriate design modifications, even high-shear systems like gear pumps can be successfully employed. Materials used in the system should exhibit chemical resistance to the UV curable material. In addition, the system should prevent light getting to the UV material. All components should be completely opaque. Even a small amount of diffused light through a lightly colored plastic can trigger curing of acrylate systems, particularly those designed for operating within the visible and UVA range. In addition, materials like copper, nickel, zinc, chromium, and lead, known to trigger UV gelling, should be avoided. Another factor to consider is compatibility with material needed to run the system like flushing compounds, lubricants, throat spray materials and the like. These need to be tested for compatibility with the pumped material. Acrylates are susceptible to Michael Addition which is a nucleophilic addition of a carbanion or a nucleophile to an alpha, beta-unsaturated carbonyl compound containing a conjugate system. Strong Nucleophiles include:
• Halide Ions: Iodide (I-), bromide (Br-), and chloride (Cl-) ions are common examples of strong nucleophiles.
• Sulfur Compounds: Thiols and thiolate ions, like alcohols and alkoxide ions but with sulfur replacing oxygen, are stronger nucleophiles because sulfur is less electronegative than oxygen.
• Amines: Primary and secondary amines are good nucleophiles. They can donate the electron pair on the nitrogen atom.
• Alkoxides: These are the conjugate bases of alcohols (RO-) and are strong nucleophiles.
• Hydride ions: These are used in reducing and are often found in compounds like lithium aluminum hydride (LiAlH4) or sodium borohydride (NaBH4).
• Grignard and organolithium reagents: These are very strong nucleophiles and are often used in carbon-carbon bond-forming reactions.
• Cyanide ions: These are also strong nucleophiles, often used in reactions to extend carbon chains.
• Carbanions: These species, which are often generated from deprotonation of carbon acids, such as malonate or acetylacetone, are strong nucleophiles.
Scale-up processes present additional complexities, such as heightened system pressures, cycling on and off which can remove air from the material, increased temperatures, and prolonged dwell times under pressure and heat. Engineers and operators should be mindful of these factors, which, in conjunction with reduced dissolved air content, could lead to premature curing. Idea systems should sit without heat or pressure.
Production Use Considerations:
During production, regular maintenance and cleaning are crucial to prevent system degradation and blockages. High-exposure components should be replaced periodically to prevent failures due to wear and tear or chemical interactions. Real-time monitoring systems to measure temperature, pressure, and dissolved air content should be incorporated, enabling timely system adjustments. Technological advancements, like smart pumps with integrated sensors, can provide early warnings of potential issues and enhance process efficiency.
The design, scale-up, and production use of acrylate UV curable systems require careful consideration of various factors, from pump selection to material choices. While the challenges can be complex, a strategic and informed approach can ensure the successful implementation of these systems in various industrial applications. As technology and material science continue to evolve, so too will the strategies for effective system design and operation, keeping the field of UV curable systems an exciting area for ongoing research and development.