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D2979-16 – Standard Test Method Technical Guide
📐 Scope and Significance
This test method, designated D2979-16, covers the measurement of pressure-sensitive tack of adhesives. It is applicable to adhesives that form a bond of measurable strength rapidly upon contact and can be removed cleanly without residue. Tack is measured as the force required to separate the adhesive and adherend at the interface shortly after contact under a defined load of known duration at a specified temperature. Values are stated in SI units as the standard, with parentheses for information only.
This method provides a quantitative measure of tack for the adhesive mass itself, suitable for pressure-sensitive adhesives on both rigid and flexible backings. It is intended for quality control and research purposes, offering a reliable metric for adhesive performance.
⚙️ Apparatus and Test Procedure
The apparatus includes a Type 304 stainless steel probe, 5.0 mm in diameter, with a tip finished to a surface roughness of 250 to 500 nm rms. A pressure-loading weight, typically an annular ring, applies a contact pressure of 9.79 ± 0.10 kPa. Optional weights can achieve pressures of 0.98, 1.96, 4.90, or 98 kPa for investigating pressure dependence. A force gage with a maximum reading indicator is used to measure the tack force.
The test procedure involves bringing the cleaned probe tip into contact with the adhesive at a controlled rate, under a fixed pressure, for a short duration at a specified temperature. The bond is then broken at a controlled rate, and tack is recorded as the maximum force required to separate the probe from the adhesive.
| 🟦 Contact Pressure | ⚡ Application |
|---|---|
| 9.79 ± 0.10 kPa (1.42 psi) | Standard test condition |
| 0.98 kPa (0.14 psi) | Optional low pressure |
| 1.96 kPa (0.28 psi) | Optional low pressure |
| 4.90 kPa (0.71 psi) | Optional low pressure |
| 98 kPa (14.2 psi) or higher | Optional high pressure |
Note: For adhesives on flexible backings or thicker than 0.25 mm, a probe with a spherical crown of 0.05 mm height and 62.5 mm radius may be used.
📊 Key Measured Properties
The primary property measured is the pressure-sensitive tack, quantified as the maximum force required to break the adhesive bond under specified conditions. This force is directly recorded by the force gage, which retains the maximum reading until reset. The test method ensures reproducibility through controlled parameters, including probe surface roughness, contact pressure, contact time, and separation rate.
Conditioning of test specimens should follow Practice E171 for flexible barrier packaging, ensuring consistent testing environments.
💡 Technical Note: Maintaining the probe surface roughness within the specified range (250–500 nm rms) is critical for accurate tack measurements. Variations can significantly affect bond formation and separation forces.
⚠️ Important: Ensure the adhesive is cleanly removable from the probe surface to avoid residue contamination, which can alter subsequent test results.
❓ Frequently Asked Questions
🔍 What is the purpose of this test method?
It provides a quantitative measure of pressure-sensitive tack for adhesives, aiding in quality control and research.
💡 What probe specifications are required?
A Type 304 stainless steel probe, 5.0 mm diameter, with a tip surface roughness of 250–500 nm rms. A spherical crown option is available for flexible backings.
⚡ What contact pressures can be used?
The standard pressure is 9.79 kPa, but optional pressures of 0.98, 1.96, 4.90, and 98 kPa can be used to study pressure effects.
📌 How is tack measured in this test?
Tack is measured as the maximum force required to break the adhesive bond when the probe is separated from the adhesive at a controlled rate.