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D3521-86 – Standard Test Method Technical Guide
📋 Scope and Definitions
This test method, designated D3521‑86 (Reapproved 2017), covers the determination of the weight of wax present as a coating on the surface of corrugated board. It is applicable to board where wax has been applied by curtain coating, roll coating, or other methods. The substrate board may or may not contain impregnating (saturating) wax within its structure. The weight of wax coating is defined as the wax present as a surface film, excluding any portion located below the surface that may have soaked into the fibrous paperboard structure.
| 🟦 Unit | 📏 Symbol | 🎯 Usage |
|---|---|---|
| Grams per square metre | g/m² | Standard SI unit for reporting wax coating |
| Pounds per thousand square feet | lb/1000 ft² | Alternative unit provided for information only |
⚠️ Important Note: If it is known that the specimen has coating wax only with no internal saturating wax, the total coating wax applied may be determined by Test Method D3344. This method is designed exclusively for surface wax measurement.
⚙️ Test Procedure and Significance
Wax coatings are applied to corrugated board to provide a better barrier against moisture or other agents as well as improved appearance or abrasion resistance. These performance features are influenced by the amount of wax present on the surface. The test method determines the surface wax amount by delaminating the coated facing to obtain a ripple‑free sheet, then scraping off the wax using a razor blade and calculating the wax removed. During most coating operations the major portion of applied congeals on the surface while a minor proportion migrates into the fibers; this method measures only the surface portion.
| 🟦 Apparatus | 📏 Specification | ⚡ Key Requirement |
|---|---|---|
| Sample‑Trimming Equipment | Trimming board or template with razor edge knife | Must cut specimens evenly with parallel sides; guillotine‑type cutter is not recommended |
| Measuring Rule | Steel‑edged rule | Accurate to within 0.5 mm |
| Razor Blades | Common single‑edge with rigid rim for finger‑holding | An adequate supply of fresh, sharp blades is required |
💡 Technical Tip: Always use fresh razor blades for each scraping operation to ensure clean removal of the surface wax and avoid cross‑contamination. Accurate measurement of specimen dimensions with the steel‑edged rule is critical for reliable weight‑per‑unit‑area calculations.
❓ Frequently Asked Questions
🔍 How does this test differ from Test Method D3344?
D3521 measures only the surface wax coating present on corrugated board, while D3344 determines the total wax content (both surface and internal saturating wax). If only coating wax is present, D3344 may be used to determine the total applied coating.
💡 Why must the coated facing be delaminated?
Delamination produces a ripple‑free sheet that allows the razor blade to scrape off the surface wax uniformly and accurately without interference from the corrugated structure beneath.
⚡ What units are standard for reporting wax coating weight?
The standard SI unit is grams per square metre (g/m²). Values in pounds per thousand square feet (lb/1000 ft²) are provided for reference only, per the exception noted in the scope.
📌 Is the method suitable for boards with internal saturating wax?
Yes, the method specifically excludes internal wax from the measurement. It only measures the wax congealed on the surface, regardless of whether the substrate contains impregnating wax.