Tensile Strength of Packing Tape – BOPP Technical Test Data
The tensile strength of packing tape is the force a finished BOPP pressure-sensitive tape withstands before the backing breaks under a defined test. The value should be read with specimen width, test direction, film gauge, conditioning, elongation, and failure location. Representative roll testing and a line trial are recommended before full use.
Why the Same Roll Can Return Different Breaking Results
The same BOPP roll can test differently as commercial-width tape and as a fresh laboratory-cut specimen. ISO 29864 allows defined cut specimens and original-width tape within method limits, while ASTM D3759/D3759M distinguishes as-received tape from specimens prepared to characterize the backing. A fresh cut may remove small slit-edge defects that can start an earlier crack.
The report should therefore identify sample width, preparation, and break location. Edge nicks, jaw misalignment, or specimen slip can create an abnormal low value that should be investigated before the batch is judged.
Before Comparing Two Tensile Numbers
Before comparing two values, match the method, specimen width, machine direction, crosshead speed, conditioning, film thickness, and sample preparation. BOPP is oriented film, so direction and test setup affect the result.
Compare several representative specimens rather than ranking grades from one isolated number, especially when storage history or operator setup differs. For the broader relationship between thickness, peel adhesion, holding power, tensile behavior and environmental limits, return to the BOPP packing tape technical specifications.
What N/25 mm Actually Tells You
Finished tape is often reported as breaking force normalized to width, such as N/25 mm. Bare BOPP film is commonly reported as tensile stress in MPa. The numbers are not directly comparable.
ASTM D3759/D3759M and ISO 29864 apply to pressure-sensitive tape breaking strength and elongation. ASTM D882 is used for thin plastic film. For backing-only MD/TD properties, the BOPP film data sheet provides the correct context.
Reference Window for Finished BOPP Tape
Published BOPP packing-tape data vary with film gauge, adhesive coat, and grade design. The values below are reference ranges, not universal acceptance limits. Project specifications should identify grade, method, direction, and sampling plan.
Reference Data Window
Read the Break, Not Only the Number
Failure location matters. Repeated central film rupture is more representative of backing behavior than a break from a damaged edge or beside a grip. Large scatter between specimens should trigger additional sampling before a material specification is changed.
Break Pattern and Verification Check
When the Laboratory Average Does Not Match the Packing Line
Laboratory tensile data do not reproduce unwind tension, line speed, tracking, blade condition, roller pressure, or repeated roll handling. During a line trial, check for off-center tracking, repeated edge tears, unusual stretch, and breakage during cut-off.
For product-family and machine-use context, review the clear carton sealing tape grades rather than selecting by breaking strength alone. Retest after changes in film grade, thickness, slitting setup, storage history, or equipment setting.
When Carton Failure Is Not a Tensile Failure
A tape can meet its tensile reference and still fail on a carton. Surface type, recycled fiber, dust, coating condition, temperature, humidity, application pressure, and dwell affect adhesive contact.
For a synthetic-rubber hot melt construction, Hot Melt Sealing Tape confirms the product structure. If failure appears after impact, vibration, cargo movement, or repeated handling, the shock-resistant packaging solution is more appropriate for separating backing rupture from carton closure and load-stability problems. Consider load weight, cargo shape, sunlight exposure, transport distance, and actual sample results before full use.
What to Record Before Retesting a Stored Roll
Storage history can affect roll condition and test repeatability. Record storage time, temperature, humidity, sunlight exposure, transport history, damaged packaging, roll deformation, and stabilization time before retesting. About 22 C and 50% RH can be used as a controlled storage reference where practical; formal conditioning should follow the selected test method.
FAQ
Why can a cut BOPP tape specimen test higher than the finished roll?
A fresh cut can have cleaner edges than a commercial slit edge. A nick or rough edge may start a crack earlier, so sample preparation and edge condition should be reported.
Can packing tape tensile strength in N/25 mm be compared directly with MPa?
No. N/25 mm is breaking force normalized to width, while MPa is stress based on cross-sectional area. Confirm whether the source is finished tape or bare BOPP film.
Why should machine direction be stated with the result?
BOPP is oriented film, so mechanical behavior depends on direction. Finished tape is commonly evaluated along the roll direction; omitting direction makes comparison less reliable.
Does higher tensile strength mean better carton adhesion?
No. Tensile strength describes the backing under pulling force. Carton adhesion also depends on adhesive chemistry, surface condition, application pressure, temperature, dwell, peel adhesion, tack, and holding performance.
When should an abnormal tensile result be retested?
Retest when failure starts at a damaged edge, occurs unusually close to a jaw, the specimen slips, conditions were uncontrolled, or one result differs markedly from the rest. Record why a sample was repeated or excluded.