Rust Prevention for Bulk Candle Tins: Zinc Primer vs. Epoxy Primer

In a humid warehouse or during overseas transportation, untreated candle tins will quickly develop surface corrosion, which will affect the quality of the candle packaging. When we produce bulk candle tins, the primers we choose are zinc primers and epoxy primers, both of which are suitable for different production scenarios. The chemical properties and protective effects of zinc-based primers and epoxy-based primers are different. Therefore, we will consider practical application factors, performance indicators, cost factors and environmental impacts in production.

Bulk candle tins corrosion and the role of primers

The core material of bulk candle tins is tinplate, which consists of a steel substrate with a thin layer of tin on its surface, relying on the sacrificial protection of tin. Once the tin layer is worn away, the steel underneath is easily oxidized to form iron oxide. If the edges of bulk candle tins are chipped during the production process, the steel edges will oxidize.

The primers used in our production serve two main functions: one is to form a strong physical barrier that isolates oxygen and moisture, and the other is to provide active corrosion inhibition. Zinc primers contain zinc-rich pigments to offer protection. In contrast, epoxy primers rely on a highly cross-linked polymer matrix to hinder the penetration of corrosive agents. I can choose the right type of primer based on the intended use environment of the candle tin.

Application process of zinc and epoxy primers

In our production process, we closely supervise the pretreatment process at every stage, including cleaning with an alkaline degreaser, rinsing, and phosphating for enhanced adhesion. First, we remove oil residues from the stamping and forming process; then, we apply a phosphate conversion film to form a micro-etching layer for mechanical bonding. Next, I will select a zinc-based or epoxy primer based on the customer’s requirements.

For zinc primers, we use a high-volume, low-pressure spray booth to ensure a uniform 15-25 micron zinc layer. After that, we bake the tins at 120°C for 20 minutes to cure the zinc pigment binder. For epoxy primers, we mix the two-component formula in precise proportions. We then spray the coating at a thickness of 50-60 microns and cure it at room temperature for 24 hours or accelerate the curing process to 80°C for 30 minutes. Quality inspectors monitor coating thickness with a magnetic pull-off gauge to verify each bulk candle tin stays within ±2 micron tolerance.

Zinc Primer vs. Epoxy Primer Performance Comparison

After application, our quality lab conducts rigorous salt spray and humidity testing to compare zinc and epoxy primers applied to bulk candle tins under accelerated corrosion conditions. In contrast, zinc-primed jars demonstrated cathodic protection, delaying the formation of red rust around the scribe edge for up to 1,000 hours. Additionally, epoxy-primed tins demonstrated superior barrier properties, with no undercutting at 500 hours in the ASTM B117 salt spray test. Both chemistries performed well, but they differed in their strengths.

Zinc primers excel at self-healing around minor coating damage, with exposed zinc flakes corroding rather than the steel. In contrast, epoxy primers offer better resistance to penetration, making them ideal for bulk candle tins stored in high-humidity climates. So, I adjust the primer choice based on the customer’s needs—for candle tins destined for the outdoor market or large-volume distribution, I recommend zinc primers. For high-end candle tins that require a perfect appearance rather than short-term storage, epoxy primers are recommended.

Cost, production efficiency and environmental impact of bulk candle tins

When choosing a primer for your bulk candle tins, in addition to performance, production costs and sustainability must be considered. Zinc primers typically cost 10-15% less than two-component epoxies and cure faster with heat, increasing production line output by up to 12%. Therefore, zinc-primed tins can achieve higher production output. Additionally, zinc primers typically contain lower volatile organic compound (VOC) content, thereby complying with environmental regulations.

However, epoxy primers can reduce rework costs by providing excellent surface quality and lower scrap rates. We conduct a life cycle cost analysis that covers raw material prices, labor hours, curing energy consumption, and waste disposal costs to develop a primer strategy that optimizes the economic and ecological goals of their bulk candle tin production.

Quality assurance and long-term reliability

At Tsing, we implement online coating thickness inspections, regular adhesion testing, and batch-by-batch salt spray verification. Additionally, we conduct quarterly field trials—deploying candle jars in real-world storage conditions to validate lab results against actual environmental exposures. We schedule weekly quality assurance reviews to analyze failure rates and optimize primer formulations or application parameters as needed, ensuring that every batch of bulk candle tins meets corrosion resistance benchmarks.

We are bringing you the best rust-prevention

Rust prevention for bulk candle tins requires careful primer selection, balancing the cathodic protection of zinc primers with the superior barrier properties of epoxy primers. For high-volume, complex shipping scenarios, I recommend zinc primers. For high-end candle jars that require a flawless finish and controlled storage conditions, I recommend using epoxy primers.