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D3708-88 – Standard Test Method Technical Guide
ASTM D3708 – 88 (Reapproved 2010) specifies a standard test method for determining the weight of hot melt wax applied to corrugated board by curtain coating. This method is critical for process control in manufacturing to ensure consistent barrier properties against moisture and other penetrants.
📐 Scope and Key Terminology
This test method covers the determination of the weight of hot melt coating applied to corrugated board by curtain coating. It is intended for routine process control in the plant. The term wax loading is defined as the weight of wax present primarily as a surface film but including the minor part embedded in surface fibers. It is expressed as weight per unit area, typically in grams per square metre or pounds per thousand square feet of board.
Related methods include Test Methods D3521, D3522, and D3344 for determining wax coating weight and content.
⚙️ Apparatus and Test Preparation
The required apparatus includes sample trimming equipment with a razor-edge knife for even cutting, a steel-edged measuring rule accurate to 0.5 mm, and test paper of good quality typing bond with about 25% cotton fibers, approximately 200 by 300 mm (8.5 by 11 in.). A carrier board of production uncoated corrugated board, not less than 450 by 750 mm (18 by 30 in.), is used. Die cut, slotted, and printed box blanks are acceptable. Pressure-sensitive tape is used to attach the test paper to the carrier board.
| 🟦 Apparatus | 📏 Specifications |
|---|---|
| Test Paper | Typing bond, ~25% cotton fibers, 200 x 300 mm (8.5 x 11 in.) |
| Carrier Board | Uncoated corrugated board, >450 x 750 mm (18 x 30 in.) |
| Measuring Rule | Steel-edged, accuracy 0.5 mm |
📊 Key Measured Properties and Procedure
The primary measurement is the total weight of wax applied. The test involves attaching a folded sheet of test paper to the production corrugated board, running the combination through the curtain coater, and subsequently determining the applied weight of wax on the sheet of paper. This method measures the total weight of wax applied, including both surface congealed wax and wax embedded in fibers.
For uniformity assessment, test combinations can be passed under the curtain at various locations across the width, such as left side, center, and right side. This helps in evaluating the evenness of the wax film applied.
The functional properties of wax coating, such as moisture barrier and abrasion resistance, are influenced by the amount of wax on the surface.
| 🎯 Property | ⚡ Test Method | 📐 Units |
|---|---|---|
| Total Wax Loading | Weight difference of test paper before and after coating | g/m² or lb/1000 ft² |
| Uniformity of Application | Multiple test locations (left, center, right) | Comparison of wax weights |
To ensure accurate results, use consistent test paper quality and handle carefully to avoid contamination. The test paper should be of uniform thickness and composition.
This standard may involve hazardous materials, operations, and equipment. Users must establish appropriate safety and health practices and determine regulatory limitations before use.
❓ Frequently Asked Questions
🔍 What is wax loading in this context?
Wax loading is the weight of wax per unit area on corrugated board, including surface film and embedded wax, expressed in g/m² or lb/1000 ft².
💡 How is the test paper used in the procedure?
A folded sheet of test paper is attached to the carrier board, passed through the curtain coater, and weighed before and after to determine wax uptake.
⚡ What are the requirements for the carrier board?
The carrier board must be production uncoated corrugated board, at least 450 x 750 mm. Die cut, slotted, and printed box blanks are acceptable.
📌 How can I measure the uniformity of wax application?
By placing test combinations at different positions under the curtain (e.g., left side, center, right side) and comparing the wax loading values.