Epoxy Resin as Undercut Filler for Steel Drums

Yang Yanchang

In addition to seam welding, the bottom and top covers of oil drums are often flattened using multiple layers of undercuts (Figure 1). However, some products feature a lighter undercut that is not fully flattened, known as a round curl (Figure 2). Whether the undercut is flattened or left as a round curl, a layer of traditional brown sugar bone glue is typically applied before the undercut to prevent leakage after the drum is formed. This method has been used for many years but comes with limitations in terms of durability and performance.

Figure 1: Flattening the Curl

Figure 2: Round Curl

In recent years, there has been an increasing demand for high-quality, long-lasting packaging solutions, especially for containers used in the transportation of sensitive materials. The appearance and structural integrity of the drums have also become more important. While minor leaks may be acceptable during short-distance transport, they are completely unacceptable for long-distance shipping or storage. Leaks can lead to serious issues such as corrosion from toxic chemicals or even fires caused by flammable solvents. As a result, the industry now prioritizes leak-proof performance as a key quality indicator.

Previously, we tried replacing the traditional red gutta percha filler with Tianjin Latex and Xiamen-made latex, but this still resulted in about 10% leakage. For chemical products like ethanolamine or formaldehyde, which are highly corrosive and expensive, even a small leak could be disastrous. Therefore, the need for a reliable and durable filler became urgent.

To address these challenges, we developed a new epoxy resin-based formulation. It includes dibutyl phthalate as a toughening agent, ethylenediamine as a curing agent, anhydrous ethanol as a diluent, and talc as a filler. This formulation proved highly effective as an undercut filler, achieving a 100% product qualification rate. It successfully resolved the long-standing issue of chronic oil leakage in steel drums.

After testing, we found that the epoxy resin filler remained firmly bonded to the metal sheets even after prolonged aging. Unlike traditional fillers, it did not crack or separate, ensuring no leakage. The mechanism behind this lies in the molecular structure of epoxy resins, which contain hydroxyl groups, ether groups, and highly reactive epoxy groups. These functional groups provide strong adhesion between the resin and the surrounding material.

As a thermosetting polymer, epoxy resin forms a stable network structure when cured. This gives it excellent chemical resistance, mechanical strength, dimensional stability, and properties like heat resistance, water resistance, and corrosion resistance. As a result, it is ideal for storing and transporting hazardous chemicals without the risk of leakage. This innovation has significantly improved the reliability and safety of steel drums in industrial applications.

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